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The commission on sewage disposal
october,~oo~
Commission on Sewage Disposal
43
THE COMMISSION ON SEWAGE DISPOSAL. ThE Commissioners appointed in 1898 to inquire and report what methods of treating and disposing of sewage may properly be adopted have issued an interim report. While many investigations remain to be completed, the Commissioners state : " W e have, however, arrived at conclusions on three questions which appear, for reasons hereafter given, to be of urgent importance, and we have therefore deemed it desirable to make a preliminary report and to publish the evidence already taken. " T h e three questions are : (1) Are some sorts of land unsuitable for the purification of sewage? (2) Is it practicable uniformly to produce by artificial processes alone an effluent which shall not putrefy, and so create a nuisance in the stream into which it is discharged? (3) What means should be adopted for securing the better protection of our rivers ?" The three conclusions at which they arrive on these questions are as follows : " 1 . Unsuitable Land.--We doubt if any land is entirely useless, but in the case of stiff clay and peat lands the power to purify sewage seems to depend on the depth of the top soil. There are, of course, numerous gradations in the depths of top soil which are met with in nature, and it is not easy to draw the line between lands which contain a sufficient depth to justify their use and lands which do not. We are, however, forced to conclude that pea~ and stiff clay lands are generally unsuitable for the purification of sewage, that their use for this purpose is always attended with difficulty, and that where the depth of top soil is very small--say 6 inches or less--the area of such lands which would be required for efficient purification would in certain cases be so great as to render land treatment impracticable. Further information with regard to this point will be available when our investigation of land treatment is completed. "2. Artificial Processes.--After carefully considering, however, the whole of the" evidence, together wi~h the results of our own work, we are satisfied that it is practicable to produce by artificial processes alone, either from sewage or from certain mixtures of sewage and trade refuse such, for example, as are met with at Leeds and Manchester, effluents which will not putrefy, which would be classed as good according to ordinary chemical standards, and which might be discharged into a stream without fear of creating a nuisance. We think, therefore, that there are cases in which
44
Commission on Sewage Disposal
t~buc He~ath
the Local Government Board would be justified in modifying, under proper safeguards, the present rule as regards the application of sewage to land. No general rule as to what these safeguards should be can be laid down at present, and indeed it will probably always be necessary that each case should be considered on its own merits. " 8 . Protection of Rivers.--We consider it of the utmost importance that the simplest possible means should be provided for adequately protecting all our rivers, and we are further of opinion that it will be desirable, probably for some time to come, that scientific experiments should be carried on in order to ascertain all the real dangers of pollution, against which they should be proreefed. In the present state of knowledge, and especially of bacteriology, it is difficult to estimate these dangers with any accuracy, and it seems quite possible that they should be either exaggerated or undervalued according to the predisposition of those who have to deal with them. An authority, guided by medical considerations, might not unnaturally be inclined to insist on a degree of purity which may ultimately prove in certain cases to be uncalled for, whi:~ another authority, with its mind fixed upon economy, might shrink from taking essential precautions. It is, perhaps, scarcely for us to say what arrangements should be made, but we are of opinion that the general protection of our rivers is a matter of such grave concern as to demand the creation of a separate Commission or a new department of the Local Government Board, which shall be a Supreme Rivers Authority, dealing with matters relating to rivers and their purification, and which, when appeal is made to them, shall have power to take action in cases where the local authorities have failed to do so." Sewage E~uents in relation to Disease. ~ The Commissioners recognise that the quality of sewage effluents must be judged not only from a chemical, but also from a bacteriological point of view ; but they do not feel justified in putting forward any recommendation thereon until the investigations which they have instituted are completed. Even at this stage they are able to point out that, as a result of a large number of examinations of effluents from sewage farms and from artificial processes, they find that while in the case of effluents from land of a kind suitable for ~he purification of sewage there are fewer micro-organisms than in the effluents from most artificial processes, yet both classes of effluents usually contain large numbers of organisms, many of which appear to be of intestinal derivation, and some of which are of a kind liable, under certain circumstances at least, to give rise to disease.
Ocl~ober,1901] T h e r m a l Death.point of B. Tuberculosis
45
They are of opinion, therefore, that such effluents must be regarded as potentially dangerous, and they are considering whether m e a n s are available and practicable for eliminating or destroying such organisms, or, at least, those giving rise to infectious diseases.
THERMAL DEATH-POINT OF THE TUBERCLE BACILLUS. THE thermal death-point of the tubercle bacillus has beeu the subject of research by a number of investigators. The subject is a very important one, on account of the large use made at the present time of pasteurized and sterilized milk. We know that boiling for a short time will destroy the tubercle bacillus, but boiled milk has many disadvantages, vie., its thin character, pronounced fiavour, and loss of nutritive and antiscorbutie qualities. To overcome these objections to boiled---/.e., sterilized--milk, pasteurization was introduced, and consists in heating the milk to a temperature of about~ 68 ° C. for twenty minutes. The question which has to be'answered is, Can pasteurization be relied upon to destroy the tubercle bacillus ? De ~ a n found that an exposure of fifteen minutes at 65° C. was required, Bang of Copenhagen considered that pasteurization could ~ot always be relied upon, and laid down the rule that milk should be heated to 85 ° C. in order to render it safe. In the Report of the Royal Commission on Tuberculosis, Woodhead's experiments gave somewhat irregular results. I n some instances, heating to 60 ° C. for twenty minutes destroyed the infectivity of tuberculous milk ; in others, the milk was still infective even after three hours' heating. These irregular results seemed to be explained by Theobald Smith's experiments (Journ. Experiment. Med., iv., 1899, p. 217), which showed that tuberculous milk was rendered non-infective by heating to 60° C. for fifteen or twenty minutes, provided no surface scum formed. In the f~m which forms when milk is heated:with free exposure to air the tubercle bacilli seem to be proreefed, and may survive heating to 60 ° C. for over an hour. Russe and Hastings have confirmed Smith's results in an exhaustive paper
(Seventeenth Annual lCep. of the Wisconsin Agvivult. Ex2eriment. Station). Their main results are as follows ; 1. An exposure of tuberculous milk in a tightly-closed commercial pasteurizer for a period of ten minutes destroyed in every case the tubercle bacillus, as determined by the inoculation of such heated milk into susceptible animals, as guinea-pigs. 2. Where milk was exposed under conditions that would enable a surface pellicle: or membrane to form on the surface, the tubercle organism is able to resist the action of heat at 140 ° F. (60 ° C.) for considerably longer periods of time. 3. Eificient pasteurization can he more readily accomplished in a closed*receptacle such as is most frequently use4 in t h e commercial treatment of milk than where the milk is treated in open bottles or open vats. 4. t t is recommended, in order to thoroughly pasteurize milk, so as to destroy any tubercle bacilli which it may contain, without in any way injuring its creaming properties or consistency, to heat the same in closed pasteurizers for a period of not less than twenty minutes at 140 ° F. (60 ° C.).---R. T. tt. in T~'eatment.
Commission on Sewage Disposal
43
THE COMMISSION ON SEWAGE DISPOSAL. ThE Commissioners appointed in 1898 to inquire and report what methods of treating and disposing of sewage may properly be adopted have issued an interim report. While many investigations remain to be completed, the Commissioners state : " W e have, however, arrived at conclusions on three questions which appear, for reasons hereafter given, to be of urgent importance, and we have therefore deemed it desirable to make a preliminary report and to publish the evidence already taken. " T h e three questions are : (1) Are some sorts of land unsuitable for the purification of sewage? (2) Is it practicable uniformly to produce by artificial processes alone an effluent which shall not putrefy, and so create a nuisance in the stream into which it is discharged? (3) What means should be adopted for securing the better protection of our rivers ?" The three conclusions at which they arrive on these questions are as follows : " 1 . Unsuitable Land.--We doubt if any land is entirely useless, but in the case of stiff clay and peat lands the power to purify sewage seems to depend on the depth of the top soil. There are, of course, numerous gradations in the depths of top soil which are met with in nature, and it is not easy to draw the line between lands which contain a sufficient depth to justify their use and lands which do not. We are, however, forced to conclude that pea~ and stiff clay lands are generally unsuitable for the purification of sewage, that their use for this purpose is always attended with difficulty, and that where the depth of top soil is very small--say 6 inches or less--the area of such lands which would be required for efficient purification would in certain cases be so great as to render land treatment impracticable. Further information with regard to this point will be available when our investigation of land treatment is completed. "2. Artificial Processes.--After carefully considering, however, the whole of the" evidence, together wi~h the results of our own work, we are satisfied that it is practicable to produce by artificial processes alone, either from sewage or from certain mixtures of sewage and trade refuse such, for example, as are met with at Leeds and Manchester, effluents which will not putrefy, which would be classed as good according to ordinary chemical standards, and which might be discharged into a stream without fear of creating a nuisance. We think, therefore, that there are cases in which
44
Commission on Sewage Disposal
t~buc He~ath
the Local Government Board would be justified in modifying, under proper safeguards, the present rule as regards the application of sewage to land. No general rule as to what these safeguards should be can be laid down at present, and indeed it will probably always be necessary that each case should be considered on its own merits. " 8 . Protection of Rivers.--We consider it of the utmost importance that the simplest possible means should be provided for adequately protecting all our rivers, and we are further of opinion that it will be desirable, probably for some time to come, that scientific experiments should be carried on in order to ascertain all the real dangers of pollution, against which they should be proreefed. In the present state of knowledge, and especially of bacteriology, it is difficult to estimate these dangers with any accuracy, and it seems quite possible that they should be either exaggerated or undervalued according to the predisposition of those who have to deal with them. An authority, guided by medical considerations, might not unnaturally be inclined to insist on a degree of purity which may ultimately prove in certain cases to be uncalled for, whi:~ another authority, with its mind fixed upon economy, might shrink from taking essential precautions. It is, perhaps, scarcely for us to say what arrangements should be made, but we are of opinion that the general protection of our rivers is a matter of such grave concern as to demand the creation of a separate Commission or a new department of the Local Government Board, which shall be a Supreme Rivers Authority, dealing with matters relating to rivers and their purification, and which, when appeal is made to them, shall have power to take action in cases where the local authorities have failed to do so." Sewage E~uents in relation to Disease. ~ The Commissioners recognise that the quality of sewage effluents must be judged not only from a chemical, but also from a bacteriological point of view ; but they do not feel justified in putting forward any recommendation thereon until the investigations which they have instituted are completed. Even at this stage they are able to point out that, as a result of a large number of examinations of effluents from sewage farms and from artificial processes, they find that while in the case of effluents from land of a kind suitable for ~he purification of sewage there are fewer micro-organisms than in the effluents from most artificial processes, yet both classes of effluents usually contain large numbers of organisms, many of which appear to be of intestinal derivation, and some of which are of a kind liable, under certain circumstances at least, to give rise to disease.
Ocl~ober,1901] T h e r m a l Death.point of B. Tuberculosis
45
They are of opinion, therefore, that such effluents must be regarded as potentially dangerous, and they are considering whether m e a n s are available and practicable for eliminating or destroying such organisms, or, at least, those giving rise to infectious diseases.
THERMAL DEATH-POINT OF THE TUBERCLE BACILLUS. THE thermal death-point of the tubercle bacillus has beeu the subject of research by a number of investigators. The subject is a very important one, on account of the large use made at the present time of pasteurized and sterilized milk. We know that boiling for a short time will destroy the tubercle bacillus, but boiled milk has many disadvantages, vie., its thin character, pronounced fiavour, and loss of nutritive and antiscorbutie qualities. To overcome these objections to boiled---/.e., sterilized--milk, pasteurization was introduced, and consists in heating the milk to a temperature of about~ 68 ° C. for twenty minutes. The question which has to be'answered is, Can pasteurization be relied upon to destroy the tubercle bacillus ? De ~ a n found that an exposure of fifteen minutes at 65° C. was required, Bang of Copenhagen considered that pasteurization could ~ot always be relied upon, and laid down the rule that milk should be heated to 85 ° C. in order to render it safe. In the Report of the Royal Commission on Tuberculosis, Woodhead's experiments gave somewhat irregular results. I n some instances, heating to 60 ° C. for twenty minutes destroyed the infectivity of tuberculous milk ; in others, the milk was still infective even after three hours' heating. These irregular results seemed to be explained by Theobald Smith's experiments (Journ. Experiment. Med., iv., 1899, p. 217), which showed that tuberculous milk was rendered non-infective by heating to 60° C. for fifteen or twenty minutes, provided no surface scum formed. In the f~m which forms when milk is heated:with free exposure to air the tubercle bacilli seem to be proreefed, and may survive heating to 60 ° C. for over an hour. Russe and Hastings have confirmed Smith's results in an exhaustive paper
(Seventeenth Annual lCep. of the Wisconsin Agvivult. Ex2eriment. Station). Their main results are as follows ; 1. An exposure of tuberculous milk in a tightly-closed commercial pasteurizer for a period of ten minutes destroyed in every case the tubercle bacillus, as determined by the inoculation of such heated milk into susceptible animals, as guinea-pigs. 2. Where milk was exposed under conditions that would enable a surface pellicle: or membrane to form on the surface, the tubercle organism is able to resist the action of heat at 140 ° F. (60 ° C.) for considerably longer periods of time. 3. Eificient pasteurization can he more readily accomplished in a closed*receptacle such as is most frequently use4 in t h e commercial treatment of milk than where the milk is treated in open bottles or open vats. 4. t t is recommended, in order to thoroughly pasteurize milk, so as to destroy any tubercle bacilli which it may contain, without in any way injuring its creaming properties or consistency, to heat the same in closed pasteurizers for a period of not less than twenty minutes at 140 ° F. (60 ° C.).---R. T. tt. in T~'eatment.