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Arsenical dips in tick eradication
ABSTRACTS AND REPORT.
morning the temperature was 102'6°, and trypanosomes were detected in the blood. The following morning there was a further rise of 1°; In the other mule the trypanosomes were introduced into the mouth and nasal cavity. A similar suspension of infected blood was used as in the previous experiment, and 5 cc. were injected into the mouth and 5 cc. into the right nasal cavity, the muzzle of the animal being elevated to avoid loss of any of the liquid. The mucosa was not touched by the syringe. On the ninth d:lY the temperature rose (rom 101° to 102'8° and trypanosomes were detected in the blood. From these experimtnts the author concludes that murrina may be transmitted during copulation. (Darling, Journ. of Experiment. Med., Vol. XV., NO.4, 1St April I9T2, pp. 367-369).
ARSENICAL DIPS IN TICK ERADICATION. THE use of dips in the eradication of ticks is indicated in those cases in which rotation methods are impracticable, either wholly or in part. Immediately it was proved th at ticks were the transmitting agent in Texas fever, experiments were commenced with the object of discovering some substance that could be relied upon to destroy them upon infested animals without doing the host any harm. It was soon discovered that ticks are very resistant, and that substances which are perfectly efficient for the destruction of other external parasites, such as lice or acari, were without the slightest effect upon ticks, unless applied in such concentration as to be injurious to the cattle. Dips con'aining lime and sulphur, tobacco, and coal-tar are practically without effect upon ticks. For several years certain kinds of crude petroleum were recognised as efficient dips, but there are a number of more or less serious objections to their use. In the first place, the particular kinds of petroleum are difficult to procure; they are expensive, bulky, liable to loss by leakage, frequently have serious effects upon the cattle treated, and produce a greasy condition of the skin. About the year 1905 experiments were commenced in the United States in which arsenic was used as the active agent in various dips. Arsenic had already been in use in other parts of the world for some time. After various mixtures had been tried the follow.ing was decided upon, and applied in practice on a large scale: white arsenic, 8 Ibs.; sodium carbonate, 24 Ibs. ; pine tar, I gallon; water up to 500 gallons (American gallons. I Imperial gallon = 1'2 American gallons). The arsenic and sodium carbonate twere dissolved by boiling in 25 to 30 gallons of water, and the solution allowed to cool somewhat. The tar was then added, and sufficient water to make 500 gallons. During 1906 about 12,000 head of cattle were dipped, and the results were in some respects highly encourag~ng. Though it appeared from the reports to be questionable whether the dip was absolutely efficacious, there was no doubt as to its highly destructive effect upon the ticks and its slight injurious effects upon cattle. r n consequence of the encouraging results obtained the Bureau of Animal Industry carried out a number of investigations in order to obtain definite data relative to the efficacy of arsenical solutions as remedies against ticks. In most of the experiments the formula was varied. The quantity of arsenic used varied from 8 to 12 Ibs., and the quantity of soda from 24 to 45 lbs. When pine tar was used it was added in the proportion of I gallon to every 500 gallons of. dip. The amount of arsenic in the various dips expressed in its equivalent of arsenic trioxide varied from '16 to '495 per cent. Chemical reaction between .the arsenic and the soda results in the
ABSTRACTS AND REPORT,
formation of sodium arsenite. The proportion of soda present in the dips is more than sufficient to produce this salt, but, since the cuticle of the ticks is softened and possibly dissolved by an excess of alkali, it is possible that the efficacy of the dip may depend in part upon the quantity of free alkali present. It is uncertain whether the tar has any definite function, but it gives body to the dip, and also serves the useful purpose of rendering the appearance and odour of the dip distinctive. The effects of the dips upon cattle in the various experiments were invariably slight. No constitutIOnal symptoms were observed except in one experiment, in which the dip used contained '476 per cent. of arsenic trioxide, and these may have been due to severe skin lesions. The calf dipped in this mixture lost considerably in weight, and did not begin to recover from the effects of the dip until a month after dipping. In another case in which the proportion of arsenic was even larger the calf showed no signs of injury save slight skin lesions. Cattle not infested with ticks dipped repeatedly at intervals of two or three weeks in dips containing about '22 per cent. of arsenic trioxide gained less in weight than other un infested cattle, but it is not certain that this was due to the dipping. None of the cattle dipped with solutions containing '16 to '24 per cent. of arsenic trioxide showed any injurious effects save slight skin le~ions, although some of them were dipped in the summer. These skin lesions made their· appearance from three to nine days after the treatment, and consisted in a more or less extensive epidermal exfoliation, unaccompanied by any inflammatory changes. Occasionally slight irritation was observed. In a number of cases the skin became somewhat thickened on certain parts of the body, namely, the escutcheon, the inner sides of the thighs, the dewlap, and neck. There was rarely any cracking of the skin. The addition of 10 per cent. of crude petroleum emulsified with soap to a dip containing '17 per cent. of arsenic trioxide caused exfoliation, cracking, and soreness of the skin, which in some cases was so severe as to cause lameness. Animals treated with the same dip before the addition of the petroleum showed none of these symptoms. Bulls appear to be more liable to injuries of the skin than cows or steers. The effects of a second dipping were always less marked than those following the first. When fresh exfoliation occurred as a result of a second dipping given within two weeks of the first, it became noticeable in from eight to thirteen days after the second dipping. It was observed that there is a great difference in susceptibility of individual animals to the same dip applied in the same way. The skin injuries also appear to depend upon the manner of applying the dip. Cattle dipped ten times with an interval of one week between the first two dippings, and of two weeks between subsequent dippings, and cattle dipped seven times at intervals of three weeks, showed scarcely any effects of the dip upon the skin. The dip used in this experiment originally contained '217 per cent. of arsenic trioxide, but the sodium arsenite became oxidised to a large extent into the arsenate, and it is possible that this is less active, and that if freshly prepared dips had been used every time the effects might have been more severe, though at the tenth dipping of one lot and at the seventh dipping of the other a freshly prepared dip containing' 2 2 per cent. of arsenic trioxide was used without producing any noticeable skin injury. ' In one experiment in which dip was used containing an equivalent of "222 per cent. arsenic trioxide with some soap, the effects on the skin, though not serious, were somewhat more marked than those usually observed following the use of simple arsenic-soda-pine tar dip containing the same percentage of arsenic. The effects of a proprietary dip, which contained soap and other ingredients of minor importance in addition to arsenic, as
166
ABSTRACTS AND REPORT.
observed in two experiments were apparently somewhat greater than those resultmg from the above-mentioned dip containing soap, or the ordinary arsenic-soda-pine tar dip. The following conclusions may be drawn from the various experiments as to the effects of arsenical dips upon cattle. Cattle may be safely dipped or sprayed with an arsenical dip containing an equivalent of '24 per cent. arsenic trioxide or less, and the treatment repeated once seven days or more later, the only injuries to the skin that may be expected being an epidermal exfoliation, associated with some slight soreness of a local character. These conclusions exclude accidents resulting from the neglect of proper precautions. Cattle are liable to suffer severely in hot weather, if driven long distances, or even if allowed to run short distances. Efficts of Arsenical Dips upon Ticks.-The results of the experiments confirm those of other observers, that ticks are very sensitive to arsenic, but it is not known by what avenues the arsenic enters the tick. W. F. Cooper states that he proved that on the application of an arsenical solution to the skin of a beast the arsenic penetrated the skin and was to be found in all the tissues, and that further this penetrat;on took place rapidly. In his experiments'a considerable amount of arsenic was found in blood taken from the heart as early as eighteen hours after dipping. Contrary to the results obtained by Cooper, a committee investigating the subject in Natal found no trace of arsenic in the muscles, liver, kidneys, or stomach of cattle dipped repeatedly and at short intervals. From the experiments of Watkins-Pitchford it appears that the frequent dipping of cattle results in an accumulation of arsenic in the skin, and that this quantity per unit area of skin is remarkably constant and cannot be materially raised by shortening the periods between dippings. He believes that the process is a vital one, and that any excess of arsenic is carried away by the blood and excreted by the kidneys. There is only incomplete evidence regarding the quantity of arsenic that may be found in the skin of an animal that has been sprayed immediately after death. According to Watkins-Pitchford the quantity present in the hair and scurf is raised, while that present in the skin is not. The quantity present in the hair and scurf is always greater than in the skin_ It has been shown by the same author in a limited number of experiments that animals that have been treated are poisonous to ticks, that the toxicity increases with the number of treatment~, and that it is less in regularly treated animals the longer the period elapsing after the last treatment. He also claims to have proved that the ticks are not killed by the arsenic present in the blood, by spraying animals all over except for a certain area on which ticks were placed, the ticks remaining unaffected. On the other hand, the poisonous effects do not appear to be due to a simple deposition of arsenic on the skin, because when ticks are permitted to attach themselves to an area of skin, on a regularly treated animat, which has been previously shaved and washed to remove any arsenic from the surface, they succumb. Arsenic has been found in the hair as long as seven months after treatment. A case is referred to in which a rainfall of 3 inches did not appreciably lower the quantity of arsenic in the coat. It is certain that the action of arsenical dips does not entirely depend upon the arsenic obtained by the ticks from the skin, for ticks removed from cattle immediately after dipping may afterwards exhibit evidence of having been acted upon by the dip. The exact mechanism of the action of arsenical dips is at present not fully understood. Female Tzcks.-It was noted that, as a rule, after cattle had been treated the number of female ticks maturing became rapidly less day by day, and that it was exceptional to find any engorged ticks present a few days after
ABSTRACTS AND REPORT.
the treatment. This indicates that the younger female ticks die before becoming engorged. In a number of experiments it was found that treated cattle were free from engorged ticks in three to nine days after treatment. The effect of the dip upon engorged ticks was shown by a controlled experiment in which three calves were used. Two were dipped and one left untreated. On the dipped calves 1340 and 1907 ticks became engorged during the first week after dipping, while on the undipped animal 968 ticks became engorged. Subsequently to the first week only 67 and 37 ticks reached the stage of engorgement on the dipped calves, whereas more than 1000 reached full maturity on the untreated one. In this instance the dip used was rather weaker than that usually employed, as it contained only '16 per cent. arsenic trioxide. Observations were made regarding the fate of engorged ticks falling from treated cattle, and these observations were controlled by similar observations on the fate of ticks falling from untreated cattle. It was noted that in some cases the ticks from treated cattle all died without ovipositing. In the majority of cases, however, some of the ticks laid eggs, the percentage so doing being as a rule low, but in very exceptional cases being as high as 100. In the control lots the percentage was almost always 100. The ticks from treated cattle almost always laid a much smaller number of eggs than those from untreated cattle. It was further observed that such eggs rarely hatched. In the few cases in which hatching occurred the larv~ appeared to be very weak and could scarcely move, some indeed being unable to complete their escape from the egg. The results obtained by immersing ticks taken from untreated cattle for two minutes in dip, were very similar to those just described. Male Ticks.-Very few male ticks were found alive on cattle more than a day or so after dipping, and it is probable that most of these were in the nymphal stage at the time of dipping. The vast majority of nymphs were found by experiment to be killed by a single treatment. In several experiments some of the nymphs survived and afterwards moulted. Observations were made regarding the fate of nymphs removed from their host at varying periods after treatment. Only a minority of these moulted. In control observ;ttion the immense majority moulted. In no instance was the survival of larv~ observed after a single treatment. It is unsafe to place any reliance upon the protective action of arsenical dips, and it should be assumed that treat(d cattle are liable to reinfection if exposed at any time after the solution has become dry on their bodies. At present arsenical dips must be considered as falling short of the ideal of perfect efficiency in that none of them has proved sufficiently efficacious to insure a tick-free condition of cattle after a single application. In spite of this such dips may be used with great advantage in the eradication of ticks. This has been demonstrated both in experimental and field observations. The practical application of the results of the experiments may be considered under the following headings :Composition of the dip. Method of application. 3. Number and frequency of applications. 4. Handling of cattle. 1.
2.
Composition of the Dtp.-Sufficient experiments have not as yet been made to enable a definite statement to be made as to the minimum percentage of arsenic required to give an arsenical dip a sufficiently high degree of efficiency to make it of practical value. It is probable that under certain conditions the strength of a dip may have to be modified on account of injurious effects.
168
ABSTRACTS AND REPORT,
For example, it may have to be made weaker in summer if dipping is repeated a number of times, The arbitrary standard of arsenic content may be taken as '22 per cent. of arsenic reckoned as arsenic trioxide, The experiments indicate that '24 per cent. may be used without injurious effects, and that a dip containing somewhat less than '2 per cent. is somewhat less efficacious than those containing that quantity or slightly more, The directions for preparing the dip so that it may conform to the standard are as follows : In preparing 500 gallons of dip, boil together for fifteen minutes TO lbs, of finely powdered white arsenic, containing not less than 99 per cent, arsenic trioxide, and 25 lbs. of sodium carbonate in not less than 25 gallons of water. Before the tar is added the temperature of the mixture should be reduced to 1400 F. by the addition of cold water. The tar should be added gradually, with constant stirring, and the bulk immediately made up to 500 gallons, The cooling of the liquid before adding the tar is important, in order to avoid a curdled appearance of the dip. If a weaker dip be required 8 lbs. of arsenic may be used. MetllOd of Application.-Arsenical dips may be used either for spraying or dipping. The former is not practicable, except in the case of very small herds, unless a spraying machine be used. These machines have proved less satisfactory than dipping vats. The use of vats is more economical than spraying pumps,' unless only a small number of animals are to be treated. A dipping vat for cattle should be at least 51 feet in depth, and, unless the animals are to be held in the vat, it should measure 40 feet in length at the surface of the dip. If a shorter vat be used, the cattle should be held in It for at least fifteen seconds, or, better, half a minute, otherwise they may get through the bath without getting wet to the skin. A steep slide at the entrance to the bath is desirable in orner to ensure a plunge that will take the cattle entirely under the surface of the bath. Number and Frequency of Applzeations.-Experiments have shown that cattle may be entirely freed from ticks by two treatments with arsenical dips. The interval between the dippings should be seven to ten days, and a fullstrength dip used. The foregoing statement applies to cattle that can be placed upon un infested ground after treatment. When cattle continue to occupy the same pasture the dipping should be repeated at intervals of not more than three weeks, this being about the time required fora larval tick to reach maturity and become engorged. Experience has shown that eradication may be achieved in this way, the probable explanation being that, even if ticks occasionally survive dipping, the number is reduced below the minimum required to insure the survival of the species. No set rule can be given as to the number of times it will be necessary to repeat the treatment, but a general rule would be to continue until the ticks had apparently disappeared, the treatment being recommenced should ticks again make their appearance. Handling of Cattle.--Cattle should not be dipped when hred or thirsty, and after treatment they should not be allowed to drain in places where the dip dripping from their bodies will form pools, or where the grass will become soaked. For a week or so after treatment the cattle should not be allowed to become overheated, nor should they be driven. After treatment cattle may be sent by rail, even though their hodies have only just become dry. When cattle are to be dipped twice special arrangements must be made to avoid reinfection. Yards and alleyways must be reserved for cattle that have been dipped twice, and must be free from ticks. Between the dippings
ABSTRACTS AND REPORT.
the cattle must be kept either in places that are known to be infested, or in places that it is not desired to keep free from infestation. After the second dipping they must be guarded against reinfestation, some suitable arrangement being made where one vat is used for both dippings that will ensure that the cattle that have been dipped once and those that have been treated twice do not have to traverse the same yards or alleys. (Ransom and Graybill, Twenty-Seventh Ann. Report, Bureau of An. Indust., 1910, pp. 267-2 8 4.)
IMMUNISATION AGAINST SWINE PLAGUE AND SWINE FEVER. from swine erysipelas, serious losses are caused annually in Austria by swine fever and the so-called chronic swine plague of young pigs. The author believes that the number of cases of swine fever is decreasing in all parts of Austria, but that the so-called swine plague is responsible for great losses. By the term swine plague is meant the disease which Ostertag looks upon as a mild chronic form of the classic swine plague, and which, on the other hand, Hutyra describes as enzootic pneumonia of young pigs. While the author was in Southern Austria investigating the diseases of pigs, cases of classic swine plague (Loeffler and Schutz) were so seldom met with that he has nothing to say with regard to it. He had, however, plenty of opportunity of studying the above-mentioned disease of young pigs and swine fever, thousands of cases coming under his notice. APART
Swine Plague. The first cases of the disease which came under the author's notice, about fifteen years ago, occurred principally on farms where the pigs were reared under bad hygienic conditions, but subsequently the disease was most frequently met with in large breeding establishments where hygienic conditions were satisfactory, but where extensive production of pure-bred animals was carried on, the animals being exclusively or almost exclusively housed. lnno instance was the author able to observe a transition from the classic swine plague to the mild chronic form, but he cannot definitely deny that the classic form of the disease is the forerunner of the chronic form. The course of the disease is constant. The young pigs commence to cough a few days after birth or after weaning. They become dull and lose their appetite. The colour of the skin becomes altered, and in the later stages is eczematous. Diarrhrea and wasting are observed, the coughing increases in severity, and in a varying proportion of cases there is slow recovery. In fatal cases death is due to exhaustion and weakness. The duration of the disease is dependent on various circumstances, such as housing, food, etc. While under unfavourable circumstances the majority of the pigs either die or become wasters, the losses under the best hygienic conditions are far less. The disease is also far more fatal during the winter than during the warmer seasons of the year. Some breeders, when the disease breaks out among their pigs in winter, allow their sows to farrow in sheds out in the open, a plentiful supply of clean dry straw cut into short lengths being supplied. By so doing the majority of the young pigs are saved; while on the same premises pigs born in dark, wet, cemented styes for the most part die of catarrhal pneumonia.
morning the temperature was 102'6°, and trypanosomes were detected in the blood. The following morning there was a further rise of 1°; In the other mule the trypanosomes were introduced into the mouth and nasal cavity. A similar suspension of infected blood was used as in the previous experiment, and 5 cc. were injected into the mouth and 5 cc. into the right nasal cavity, the muzzle of the animal being elevated to avoid loss of any of the liquid. The mucosa was not touched by the syringe. On the ninth d:lY the temperature rose (rom 101° to 102'8° and trypanosomes were detected in the blood. From these experimtnts the author concludes that murrina may be transmitted during copulation. (Darling, Journ. of Experiment. Med., Vol. XV., NO.4, 1St April I9T2, pp. 367-369).
ARSENICAL DIPS IN TICK ERADICATION. THE use of dips in the eradication of ticks is indicated in those cases in which rotation methods are impracticable, either wholly or in part. Immediately it was proved th at ticks were the transmitting agent in Texas fever, experiments were commenced with the object of discovering some substance that could be relied upon to destroy them upon infested animals without doing the host any harm. It was soon discovered that ticks are very resistant, and that substances which are perfectly efficient for the destruction of other external parasites, such as lice or acari, were without the slightest effect upon ticks, unless applied in such concentration as to be injurious to the cattle. Dips con'aining lime and sulphur, tobacco, and coal-tar are practically without effect upon ticks. For several years certain kinds of crude petroleum were recognised as efficient dips, but there are a number of more or less serious objections to their use. In the first place, the particular kinds of petroleum are difficult to procure; they are expensive, bulky, liable to loss by leakage, frequently have serious effects upon the cattle treated, and produce a greasy condition of the skin. About the year 1905 experiments were commenced in the United States in which arsenic was used as the active agent in various dips. Arsenic had already been in use in other parts of the world for some time. After various mixtures had been tried the follow.ing was decided upon, and applied in practice on a large scale: white arsenic, 8 Ibs.; sodium carbonate, 24 Ibs. ; pine tar, I gallon; water up to 500 gallons (American gallons. I Imperial gallon = 1'2 American gallons). The arsenic and sodium carbonate twere dissolved by boiling in 25 to 30 gallons of water, and the solution allowed to cool somewhat. The tar was then added, and sufficient water to make 500 gallons. During 1906 about 12,000 head of cattle were dipped, and the results were in some respects highly encourag~ng. Though it appeared from the reports to be questionable whether the dip was absolutely efficacious, there was no doubt as to its highly destructive effect upon the ticks and its slight injurious effects upon cattle. r n consequence of the encouraging results obtained the Bureau of Animal Industry carried out a number of investigations in order to obtain definite data relative to the efficacy of arsenical solutions as remedies against ticks. In most of the experiments the formula was varied. The quantity of arsenic used varied from 8 to 12 Ibs., and the quantity of soda from 24 to 45 lbs. When pine tar was used it was added in the proportion of I gallon to every 500 gallons of. dip. The amount of arsenic in the various dips expressed in its equivalent of arsenic trioxide varied from '16 to '495 per cent. Chemical reaction between .the arsenic and the soda results in the
ABSTRACTS AND REPORT,
formation of sodium arsenite. The proportion of soda present in the dips is more than sufficient to produce this salt, but, since the cuticle of the ticks is softened and possibly dissolved by an excess of alkali, it is possible that the efficacy of the dip may depend in part upon the quantity of free alkali present. It is uncertain whether the tar has any definite function, but it gives body to the dip, and also serves the useful purpose of rendering the appearance and odour of the dip distinctive. The effects of the dips upon cattle in the various experiments were invariably slight. No constitutIOnal symptoms were observed except in one experiment, in which the dip used contained '476 per cent. of arsenic trioxide, and these may have been due to severe skin lesions. The calf dipped in this mixture lost considerably in weight, and did not begin to recover from the effects of the dip until a month after dipping. In another case in which the proportion of arsenic was even larger the calf showed no signs of injury save slight skin lesions. Cattle not infested with ticks dipped repeatedly at intervals of two or three weeks in dips containing about '22 per cent. of arsenic trioxide gained less in weight than other un infested cattle, but it is not certain that this was due to the dipping. None of the cattle dipped with solutions containing '16 to '24 per cent. of arsenic trioxide showed any injurious effects save slight skin le~ions, although some of them were dipped in the summer. These skin lesions made their· appearance from three to nine days after the treatment, and consisted in a more or less extensive epidermal exfoliation, unaccompanied by any inflammatory changes. Occasionally slight irritation was observed. In a number of cases the skin became somewhat thickened on certain parts of the body, namely, the escutcheon, the inner sides of the thighs, the dewlap, and neck. There was rarely any cracking of the skin. The addition of 10 per cent. of crude petroleum emulsified with soap to a dip containing '17 per cent. of arsenic trioxide caused exfoliation, cracking, and soreness of the skin, which in some cases was so severe as to cause lameness. Animals treated with the same dip before the addition of the petroleum showed none of these symptoms. Bulls appear to be more liable to injuries of the skin than cows or steers. The effects of a second dipping were always less marked than those following the first. When fresh exfoliation occurred as a result of a second dipping given within two weeks of the first, it became noticeable in from eight to thirteen days after the second dipping. It was observed that there is a great difference in susceptibility of individual animals to the same dip applied in the same way. The skin injuries also appear to depend upon the manner of applying the dip. Cattle dipped ten times with an interval of one week between the first two dippings, and of two weeks between subsequent dippings, and cattle dipped seven times at intervals of three weeks, showed scarcely any effects of the dip upon the skin. The dip used in this experiment originally contained '217 per cent. of arsenic trioxide, but the sodium arsenite became oxidised to a large extent into the arsenate, and it is possible that this is less active, and that if freshly prepared dips had been used every time the effects might have been more severe, though at the tenth dipping of one lot and at the seventh dipping of the other a freshly prepared dip containing' 2 2 per cent. of arsenic trioxide was used without producing any noticeable skin injury. ' In one experiment in which dip was used containing an equivalent of "222 per cent. arsenic trioxide with some soap, the effects on the skin, though not serious, were somewhat more marked than those usually observed following the use of simple arsenic-soda-pine tar dip containing the same percentage of arsenic. The effects of a proprietary dip, which contained soap and other ingredients of minor importance in addition to arsenic, as
166
ABSTRACTS AND REPORT.
observed in two experiments were apparently somewhat greater than those resultmg from the above-mentioned dip containing soap, or the ordinary arsenic-soda-pine tar dip. The following conclusions may be drawn from the various experiments as to the effects of arsenical dips upon cattle. Cattle may be safely dipped or sprayed with an arsenical dip containing an equivalent of '24 per cent. arsenic trioxide or less, and the treatment repeated once seven days or more later, the only injuries to the skin that may be expected being an epidermal exfoliation, associated with some slight soreness of a local character. These conclusions exclude accidents resulting from the neglect of proper precautions. Cattle are liable to suffer severely in hot weather, if driven long distances, or even if allowed to run short distances. Efficts of Arsenical Dips upon Ticks.-The results of the experiments confirm those of other observers, that ticks are very sensitive to arsenic, but it is not known by what avenues the arsenic enters the tick. W. F. Cooper states that he proved that on the application of an arsenical solution to the skin of a beast the arsenic penetrated the skin and was to be found in all the tissues, and that further this penetrat;on took place rapidly. In his experiments'a considerable amount of arsenic was found in blood taken from the heart as early as eighteen hours after dipping. Contrary to the results obtained by Cooper, a committee investigating the subject in Natal found no trace of arsenic in the muscles, liver, kidneys, or stomach of cattle dipped repeatedly and at short intervals. From the experiments of Watkins-Pitchford it appears that the frequent dipping of cattle results in an accumulation of arsenic in the skin, and that this quantity per unit area of skin is remarkably constant and cannot be materially raised by shortening the periods between dippings. He believes that the process is a vital one, and that any excess of arsenic is carried away by the blood and excreted by the kidneys. There is only incomplete evidence regarding the quantity of arsenic that may be found in the skin of an animal that has been sprayed immediately after death. According to Watkins-Pitchford the quantity present in the hair and scurf is raised, while that present in the skin is not. The quantity present in the hair and scurf is always greater than in the skin_ It has been shown by the same author in a limited number of experiments that animals that have been treated are poisonous to ticks, that the toxicity increases with the number of treatment~, and that it is less in regularly treated animals the longer the period elapsing after the last treatment. He also claims to have proved that the ticks are not killed by the arsenic present in the blood, by spraying animals all over except for a certain area on which ticks were placed, the ticks remaining unaffected. On the other hand, the poisonous effects do not appear to be due to a simple deposition of arsenic on the skin, because when ticks are permitted to attach themselves to an area of skin, on a regularly treated animat, which has been previously shaved and washed to remove any arsenic from the surface, they succumb. Arsenic has been found in the hair as long as seven months after treatment. A case is referred to in which a rainfall of 3 inches did not appreciably lower the quantity of arsenic in the coat. It is certain that the action of arsenical dips does not entirely depend upon the arsenic obtained by the ticks from the skin, for ticks removed from cattle immediately after dipping may afterwards exhibit evidence of having been acted upon by the dip. The exact mechanism of the action of arsenical dips is at present not fully understood. Female Tzcks.-It was noted that, as a rule, after cattle had been treated the number of female ticks maturing became rapidly less day by day, and that it was exceptional to find any engorged ticks present a few days after
ABSTRACTS AND REPORT.
the treatment. This indicates that the younger female ticks die before becoming engorged. In a number of experiments it was found that treated cattle were free from engorged ticks in three to nine days after treatment. The effect of the dip upon engorged ticks was shown by a controlled experiment in which three calves were used. Two were dipped and one left untreated. On the dipped calves 1340 and 1907 ticks became engorged during the first week after dipping, while on the undipped animal 968 ticks became engorged. Subsequently to the first week only 67 and 37 ticks reached the stage of engorgement on the dipped calves, whereas more than 1000 reached full maturity on the untreated one. In this instance the dip used was rather weaker than that usually employed, as it contained only '16 per cent. arsenic trioxide. Observations were made regarding the fate of engorged ticks falling from treated cattle, and these observations were controlled by similar observations on the fate of ticks falling from untreated cattle. It was noted that in some cases the ticks from treated cattle all died without ovipositing. In the majority of cases, however, some of the ticks laid eggs, the percentage so doing being as a rule low, but in very exceptional cases being as high as 100. In the control lots the percentage was almost always 100. The ticks from treated cattle almost always laid a much smaller number of eggs than those from untreated cattle. It was further observed that such eggs rarely hatched. In the few cases in which hatching occurred the larv~ appeared to be very weak and could scarcely move, some indeed being unable to complete their escape from the egg. The results obtained by immersing ticks taken from untreated cattle for two minutes in dip, were very similar to those just described. Male Ticks.-Very few male ticks were found alive on cattle more than a day or so after dipping, and it is probable that most of these were in the nymphal stage at the time of dipping. The vast majority of nymphs were found by experiment to be killed by a single treatment. In several experiments some of the nymphs survived and afterwards moulted. Observations were made regarding the fate of nymphs removed from their host at varying periods after treatment. Only a minority of these moulted. In control observ;ttion the immense majority moulted. In no instance was the survival of larv~ observed after a single treatment. It is unsafe to place any reliance upon the protective action of arsenical dips, and it should be assumed that treat(d cattle are liable to reinfection if exposed at any time after the solution has become dry on their bodies. At present arsenical dips must be considered as falling short of the ideal of perfect efficiency in that none of them has proved sufficiently efficacious to insure a tick-free condition of cattle after a single application. In spite of this such dips may be used with great advantage in the eradication of ticks. This has been demonstrated both in experimental and field observations. The practical application of the results of the experiments may be considered under the following headings :Composition of the dip. Method of application. 3. Number and frequency of applications. 4. Handling of cattle. 1.
2.
Composition of the Dtp.-Sufficient experiments have not as yet been made to enable a definite statement to be made as to the minimum percentage of arsenic required to give an arsenical dip a sufficiently high degree of efficiency to make it of practical value. It is probable that under certain conditions the strength of a dip may have to be modified on account of injurious effects.
168
ABSTRACTS AND REPORT,
For example, it may have to be made weaker in summer if dipping is repeated a number of times, The arbitrary standard of arsenic content may be taken as '22 per cent. of arsenic reckoned as arsenic trioxide, The experiments indicate that '24 per cent. may be used without injurious effects, and that a dip containing somewhat less than '2 per cent. is somewhat less efficacious than those containing that quantity or slightly more, The directions for preparing the dip so that it may conform to the standard are as follows : In preparing 500 gallons of dip, boil together for fifteen minutes TO lbs, of finely powdered white arsenic, containing not less than 99 per cent, arsenic trioxide, and 25 lbs. of sodium carbonate in not less than 25 gallons of water. Before the tar is added the temperature of the mixture should be reduced to 1400 F. by the addition of cold water. The tar should be added gradually, with constant stirring, and the bulk immediately made up to 500 gallons, The cooling of the liquid before adding the tar is important, in order to avoid a curdled appearance of the dip. If a weaker dip be required 8 lbs. of arsenic may be used. MetllOd of Application.-Arsenical dips may be used either for spraying or dipping. The former is not practicable, except in the case of very small herds, unless a spraying machine be used. These machines have proved less satisfactory than dipping vats. The use of vats is more economical than spraying pumps,' unless only a small number of animals are to be treated. A dipping vat for cattle should be at least 51 feet in depth, and, unless the animals are to be held in the vat, it should measure 40 feet in length at the surface of the dip. If a shorter vat be used, the cattle should be held in It for at least fifteen seconds, or, better, half a minute, otherwise they may get through the bath without getting wet to the skin. A steep slide at the entrance to the bath is desirable in orner to ensure a plunge that will take the cattle entirely under the surface of the bath. Number and Frequency of Applzeations.-Experiments have shown that cattle may be entirely freed from ticks by two treatments with arsenical dips. The interval between the dippings should be seven to ten days, and a fullstrength dip used. The foregoing statement applies to cattle that can be placed upon un infested ground after treatment. When cattle continue to occupy the same pasture the dipping should be repeated at intervals of not more than three weeks, this being about the time required fora larval tick to reach maturity and become engorged. Experience has shown that eradication may be achieved in this way, the probable explanation being that, even if ticks occasionally survive dipping, the number is reduced below the minimum required to insure the survival of the species. No set rule can be given as to the number of times it will be necessary to repeat the treatment, but a general rule would be to continue until the ticks had apparently disappeared, the treatment being recommenced should ticks again make their appearance. Handling of Cattle.--Cattle should not be dipped when hred or thirsty, and after treatment they should not be allowed to drain in places where the dip dripping from their bodies will form pools, or where the grass will become soaked. For a week or so after treatment the cattle should not be allowed to become overheated, nor should they be driven. After treatment cattle may be sent by rail, even though their hodies have only just become dry. When cattle are to be dipped twice special arrangements must be made to avoid reinfection. Yards and alleyways must be reserved for cattle that have been dipped twice, and must be free from ticks. Between the dippings
ABSTRACTS AND REPORT.
the cattle must be kept either in places that are known to be infested, or in places that it is not desired to keep free from infestation. After the second dipping they must be guarded against reinfestation, some suitable arrangement being made where one vat is used for both dippings that will ensure that the cattle that have been dipped once and those that have been treated twice do not have to traverse the same yards or alleys. (Ransom and Graybill, Twenty-Seventh Ann. Report, Bureau of An. Indust., 1910, pp. 267-2 8 4.)
IMMUNISATION AGAINST SWINE PLAGUE AND SWINE FEVER. from swine erysipelas, serious losses are caused annually in Austria by swine fever and the so-called chronic swine plague of young pigs. The author believes that the number of cases of swine fever is decreasing in all parts of Austria, but that the so-called swine plague is responsible for great losses. By the term swine plague is meant the disease which Ostertag looks upon as a mild chronic form of the classic swine plague, and which, on the other hand, Hutyra describes as enzootic pneumonia of young pigs. While the author was in Southern Austria investigating the diseases of pigs, cases of classic swine plague (Loeffler and Schutz) were so seldom met with that he has nothing to say with regard to it. He had, however, plenty of opportunity of studying the above-mentioned disease of young pigs and swine fever, thousands of cases coming under his notice. APART
Swine Plague. The first cases of the disease which came under the author's notice, about fifteen years ago, occurred principally on farms where the pigs were reared under bad hygienic conditions, but subsequently the disease was most frequently met with in large breeding establishments where hygienic conditions were satisfactory, but where extensive production of pure-bred animals was carried on, the animals being exclusively or almost exclusively housed. lnno instance was the author able to observe a transition from the classic swine plague to the mild chronic form, but he cannot definitely deny that the classic form of the disease is the forerunner of the chronic form. The course of the disease is constant. The young pigs commence to cough a few days after birth or after weaning. They become dull and lose their appetite. The colour of the skin becomes altered, and in the later stages is eczematous. Diarrhrea and wasting are observed, the coughing increases in severity, and in a varying proportion of cases there is slow recovery. In fatal cases death is due to exhaustion and weakness. The duration of the disease is dependent on various circumstances, such as housing, food, etc. While under unfavourable circumstances the majority of the pigs either die or become wasters, the losses under the best hygienic conditions are far less. The disease is also far more fatal during the winter than during the warmer seasons of the year. Some breeders, when the disease breaks out among their pigs in winter, allow their sows to farrow in sheds out in the open, a plentiful supply of clean dry straw cut into short lengths being supplied. By so doing the majority of the young pigs are saved; while on the same premises pigs born in dark, wet, cemented styes for the most part die of catarrhal pneumonia.