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Experimental Investigations Regarding the Development of Fasciola Hepatica
ABSTRACTS.
Small round forms were less numerous than the oval or bacillary forms, but more numerous than the piriform parasites, and corresponded with the young stages of the Theileria. They measured '5 to '7 microns in diameter, and were composed almost exclusively of chromatin. The cross-forms were identical with those of Theileria; each was formed of four rounded elements measuring about '3 microns in diame"ter, with the chromatin turned towards the centre. Binary division occurs in the bacillary forms, and in the oval forms the chromatin divides to form three nuclei. (Fran
EXPERIMENTAL INVESTIGATIONS REGARDING THE DEVELOPMENT OF FASCIOLA HEPATICA. IT is pointed out by the authors that although it is admitted that animals and man become infested by the ingestion of plants carrying the encysted cercaria::, or of the snail which harbours the larva::, no demonstration of this direct method of infestation has ever been furnished. In May 1911 they received a number of small snails (Limna::a truncatula) from a watering pond that was frequented by sheep affected with distomatosis. The majority of these harboured redia:: of Fasciola hepatica enclosing cercaria::. Eighteen of these snails, the shells of which were simply cracked, were administered to a lamb about three months old, which had been born and bred at the School at Alfort. Fifty-two days later the animal was killed. At the time of slaughter the lamb appeared to be in good health. At the post-mortem it was found that the muscular tissue was cedematous, the liver was somewhat friable, but there were no lesions save in the left lobe, which showed a large number of tracks made by the parasite. The flukes collected measured on an average 8 by 3 millimetres. They were not ovigerous. According to Thomas (1882) a period of at least six weeks is necessary before flukes ingested by sheep are capable of laying eggs. In the present experiment this period was exceeded by ten days. The authors state that they have made other observations which appear to agree with this. In one instance an infected animal was protected ·from all fresh infection and killed after five weeks. Among the flukes found were some measuring only 9 millimetres, and a single specimen measuring only 4. The authors considered the possibility that the massive invasion had lead to an arrest of development of the parasites. In view of the fact that the young flukes occurred in the parenchyma of the liver and not in the bile ducts, it appeared to be probable that the invasion of the liver took place by way of the circulation and not by way of the bile duct. There are other points which lend support to this view. Thus, in cases of massive natural infestation there is observed phlebitis of the hepatic veins, and even of the posterior vena cava. Cases are on record in which the parasite has been found in sucking lambs and calves, and Frommann records their presence in a fcetus in a ewe. There are numerous records of the occurrence of flukes in the blood-vessels, heart, and organs other than the liver, both in man and in animals. , In any case, evidence has been obtained by the authors that the sheep E
66
ABSTRACTS.
may become infested by the ingestion of snails harbouring redire containing cercarire, and encysted cercarire were observed in snails from the batch used in the experiment. The measurement of the flukes found in their experimental animal lead the authors to think that the period necessary for their full development is about twice that suggested by Thomas, i.e., three months. The parasites in the liver are able to survive for a much longer time than is generally supposed. It has been said that the flukes which gain access to the liver in the autumn are expelled during the following Mayor June, but the authors have found them in the bile ducts of a sheep protected against fresh infestation nearly three years later. It is quite easy to follow the encystment of the cercarire under the microscope. When a snail is torn open under water numbers of cercarire can be seen freeing themselves and swimming about actively. Violent movements are executed by the tail, the anterior portion of the body becomes elongated to a variable extent, and the body constantly undergoes changes in shape. The two branches of the intestine are to a great extent concealed under bands of cystogenic cells, but on their outer side they show about a dozen prominences, which are probably the points of origin of the intestinal ramifications found in the adults. Gradually the cercarire come to rest on the wall of the vessel. When at Test they measure from 240 to 270 microns in length by 215 to 250 in width. The tail varies from 430 to 570 microns. After a short interval granulations of the cystogenic cells appear on the surface, giving the parasites a studded appearance. The tail is shed after an interval of five minutes to half an hour. The detached tails continue to execute movements for a long time, and the encysted cercarire do not immediately cease to show contractile movements. The cysts, which appear black by transmitted light and white by reflected light, measure from 250 to 350 microns in diameter, and are nearly round. The envelope measures from 9 to 17 microns in thickness. If pieces of cane be placed in the water, the cercarire may he observed to attach themselves and become encysted, some at the surface of the liquid and others at a distance below. The fixation is not at all firm, as a slight current in the water is sufficient to cause detachment. By exerting slight pressure on a cyst, the young fluke may be made to emerge. At this stage the parasites measure about 350 microns in length by 300 in width . The question arises whether the ingestion of cercarire is the only method of development. The origin of this question lies in the fact that at the post-mortem examination of animals, and particularly bovines, affected with fluke there are sometimes found a considerable number of parasites which have burrowed into the substance of the liver in various directions, suggesting that there is an actual multiplication of the parasites there. The experiments of Katsurada and Hashegawa, establishing the penetration of Schistosoma japonicum through the skin and their multiplication in the interior of the body, lend support to possibility of this idea, and at the same time indicate the method by which verification might be sought. I. Numerous ciliated embryos which had just been liberated, and which were very active, were kept in contact with shaved areas of skin on two rabbits for several hours. When killed 59 and 231 days later there was no evidence of infestation. 2. Similar embryos were injected subcutaneously into five rabbits. When killed after similar periods the results were again found to be negative. 3. Subcutaneous injections into a goat, which died twenty-five days later of tuberculosis, and into a kid eight days old yielded negative results.
ABSTRACTS.
4. Similar negative results were obtained with two rabbits killed 100 days after ingesting embryos. From these experiments it would appear that the liver fluke cannot develop from embryos introduced directly into the host. (Railliet, Moussu, and Henry, Receuil de MM. Vet., Vol. XC., No. I, 15th January 1913, pp. 1-6.)
THE PROPHYLAXIS, SERUM THERAPY, AND SEROVACCINATION OF CONTAGIOUS AGALAXIA. IT would appear that this disease has not attracted very much attention in France, not because the losses for which it is responsible are inconsiderable, but, apparently, because it attacks sheep and goats, to attend to which the veterinarian is seldom called upon, because it has little tendency to spread outside certain districts, and because it is particularly in mountainous districts that the disease is met with. In the author's opinion special interest attaches to the disease because of it!> peculiar nature, there being no other disease that in the least degree resembles it. The name is not at all descriptive of the disease, as the mammary gland is one of the least frequent seats of lesions, but it is retained by the author as it has the sanction of custom, and he has not been able to suggest any sufficiently precise term to replace it. The difficulty of finding a succinct term for the disease is realised when it is remembered that the condition is a general one, with lesions in the mammary gland, eye, joints, and skin. References to the disease in French literature are of the scantiest. In Switzerland the condition has been studied by Hess and Guillbeau, and in Italy, where the disease is of the utmost importance, it has received attention from Oreste, Marra, Celli, and de Blasi. Authorities agree that it is practically impossible to calculate the loss occasioned by the disease, but that the mortality is insignificant. In France the disease is certainly less widely spread than in Italy, but sometimes it assume s a very severe form, causing a mortality of 30-40 per cent., besides occasioning great loss of condition in the survivors. In the author's opinion the common method of natural infection is by way of the alimentary canaL In view of 'the fact that there is in the majority of cases no escape of secretion from an infected mammary gland during the development of the lesions, the question arises as to how the food becomes contaminated. The author has obtained evidence that the lachrymal secretion from eyes showing no ulceration of the cornea is virulent, and he believes that it is through the medium of this secretion that the food becomes contaminated. According to Celli and de Blasi, the virus reaches its maximum degree of virulence during the first stage of the disease, and Marra states that the milk is not virulent save at the onset of fever. The evidence obtained by the author is at variance, however, with these views, as he has been able to show that the mammary secretion may be infective for months, even up to the time when there is complete atrophy of the gland-in one case a period of seven months. That milk drawn from the gland does not rapidly lose virulence was shown by the fact that some infective milk was kept for eight days at room temperature during the month of August, and when this was injected into the teat of a goat a typical attack of the disease was produced.
Small round forms were less numerous than the oval or bacillary forms, but more numerous than the piriform parasites, and corresponded with the young stages of the Theileria. They measured '5 to '7 microns in diameter, and were composed almost exclusively of chromatin. The cross-forms were identical with those of Theileria; each was formed of four rounded elements measuring about '3 microns in diame"ter, with the chromatin turned towards the centre. Binary division occurs in the bacillary forms, and in the oval forms the chromatin divides to form three nuclei. (Fran
EXPERIMENTAL INVESTIGATIONS REGARDING THE DEVELOPMENT OF FASCIOLA HEPATICA. IT is pointed out by the authors that although it is admitted that animals and man become infested by the ingestion of plants carrying the encysted cercaria::, or of the snail which harbours the larva::, no demonstration of this direct method of infestation has ever been furnished. In May 1911 they received a number of small snails (Limna::a truncatula) from a watering pond that was frequented by sheep affected with distomatosis. The majority of these harboured redia:: of Fasciola hepatica enclosing cercaria::. Eighteen of these snails, the shells of which were simply cracked, were administered to a lamb about three months old, which had been born and bred at the School at Alfort. Fifty-two days later the animal was killed. At the time of slaughter the lamb appeared to be in good health. At the post-mortem it was found that the muscular tissue was cedematous, the liver was somewhat friable, but there were no lesions save in the left lobe, which showed a large number of tracks made by the parasite. The flukes collected measured on an average 8 by 3 millimetres. They were not ovigerous. According to Thomas (1882) a period of at least six weeks is necessary before flukes ingested by sheep are capable of laying eggs. In the present experiment this period was exceeded by ten days. The authors state that they have made other observations which appear to agree with this. In one instance an infected animal was protected ·from all fresh infection and killed after five weeks. Among the flukes found were some measuring only 9 millimetres, and a single specimen measuring only 4. The authors considered the possibility that the massive invasion had lead to an arrest of development of the parasites. In view of the fact that the young flukes occurred in the parenchyma of the liver and not in the bile ducts, it appeared to be probable that the invasion of the liver took place by way of the circulation and not by way of the bile duct. There are other points which lend support to this view. Thus, in cases of massive natural infestation there is observed phlebitis of the hepatic veins, and even of the posterior vena cava. Cases are on record in which the parasite has been found in sucking lambs and calves, and Frommann records their presence in a fcetus in a ewe. There are numerous records of the occurrence of flukes in the blood-vessels, heart, and organs other than the liver, both in man and in animals. , In any case, evidence has been obtained by the authors that the sheep E
66
ABSTRACTS.
may become infested by the ingestion of snails harbouring redire containing cercarire, and encysted cercarire were observed in snails from the batch used in the experiment. The measurement of the flukes found in their experimental animal lead the authors to think that the period necessary for their full development is about twice that suggested by Thomas, i.e., three months. The parasites in the liver are able to survive for a much longer time than is generally supposed. It has been said that the flukes which gain access to the liver in the autumn are expelled during the following Mayor June, but the authors have found them in the bile ducts of a sheep protected against fresh infestation nearly three years later. It is quite easy to follow the encystment of the cercarire under the microscope. When a snail is torn open under water numbers of cercarire can be seen freeing themselves and swimming about actively. Violent movements are executed by the tail, the anterior portion of the body becomes elongated to a variable extent, and the body constantly undergoes changes in shape. The two branches of the intestine are to a great extent concealed under bands of cystogenic cells, but on their outer side they show about a dozen prominences, which are probably the points of origin of the intestinal ramifications found in the adults. Gradually the cercarire come to rest on the wall of the vessel. When at Test they measure from 240 to 270 microns in length by 215 to 250 in width. The tail varies from 430 to 570 microns. After a short interval granulations of the cystogenic cells appear on the surface, giving the parasites a studded appearance. The tail is shed after an interval of five minutes to half an hour. The detached tails continue to execute movements for a long time, and the encysted cercarire do not immediately cease to show contractile movements. The cysts, which appear black by transmitted light and white by reflected light, measure from 250 to 350 microns in diameter, and are nearly round. The envelope measures from 9 to 17 microns in thickness. If pieces of cane be placed in the water, the cercarire may he observed to attach themselves and become encysted, some at the surface of the liquid and others at a distance below. The fixation is not at all firm, as a slight current in the water is sufficient to cause detachment. By exerting slight pressure on a cyst, the young fluke may be made to emerge. At this stage the parasites measure about 350 microns in length by 300 in width . The question arises whether the ingestion of cercarire is the only method of development. The origin of this question lies in the fact that at the post-mortem examination of animals, and particularly bovines, affected with fluke there are sometimes found a considerable number of parasites which have burrowed into the substance of the liver in various directions, suggesting that there is an actual multiplication of the parasites there. The experiments of Katsurada and Hashegawa, establishing the penetration of Schistosoma japonicum through the skin and their multiplication in the interior of the body, lend support to possibility of this idea, and at the same time indicate the method by which verification might be sought. I. Numerous ciliated embryos which had just been liberated, and which were very active, were kept in contact with shaved areas of skin on two rabbits for several hours. When killed 59 and 231 days later there was no evidence of infestation. 2. Similar embryos were injected subcutaneously into five rabbits. When killed after similar periods the results were again found to be negative. 3. Subcutaneous injections into a goat, which died twenty-five days later of tuberculosis, and into a kid eight days old yielded negative results.
ABSTRACTS.
4. Similar negative results were obtained with two rabbits killed 100 days after ingesting embryos. From these experiments it would appear that the liver fluke cannot develop from embryos introduced directly into the host. (Railliet, Moussu, and Henry, Receuil de MM. Vet., Vol. XC., No. I, 15th January 1913, pp. 1-6.)
THE PROPHYLAXIS, SERUM THERAPY, AND SEROVACCINATION OF CONTAGIOUS AGALAXIA. IT would appear that this disease has not attracted very much attention in France, not because the losses for which it is responsible are inconsiderable, but, apparently, because it attacks sheep and goats, to attend to which the veterinarian is seldom called upon, because it has little tendency to spread outside certain districts, and because it is particularly in mountainous districts that the disease is met with. In the author's opinion special interest attaches to the disease because of it!> peculiar nature, there being no other disease that in the least degree resembles it. The name is not at all descriptive of the disease, as the mammary gland is one of the least frequent seats of lesions, but it is retained by the author as it has the sanction of custom, and he has not been able to suggest any sufficiently precise term to replace it. The difficulty of finding a succinct term for the disease is realised when it is remembered that the condition is a general one, with lesions in the mammary gland, eye, joints, and skin. References to the disease in French literature are of the scantiest. In Switzerland the condition has been studied by Hess and Guillbeau, and in Italy, where the disease is of the utmost importance, it has received attention from Oreste, Marra, Celli, and de Blasi. Authorities agree that it is practically impossible to calculate the loss occasioned by the disease, but that the mortality is insignificant. In France the disease is certainly less widely spread than in Italy, but sometimes it assume s a very severe form, causing a mortality of 30-40 per cent., besides occasioning great loss of condition in the survivors. In the author's opinion the common method of natural infection is by way of the alimentary canaL In view of 'the fact that there is in the majority of cases no escape of secretion from an infected mammary gland during the development of the lesions, the question arises as to how the food becomes contaminated. The author has obtained evidence that the lachrymal secretion from eyes showing no ulceration of the cornea is virulent, and he believes that it is through the medium of this secretion that the food becomes contaminated. According to Celli and de Blasi, the virus reaches its maximum degree of virulence during the first stage of the disease, and Marra states that the milk is not virulent save at the onset of fever. The evidence obtained by the author is at variance, however, with these views, as he has been able to show that the mammary secretion may be infective for months, even up to the time when there is complete atrophy of the gland-in one case a period of seven months. That milk drawn from the gland does not rapidly lose virulence was shown by the fact that some infective milk was kept for eight days at room temperature during the month of August, and when this was injected into the teat of a goat a typical attack of the disease was produced.