July 1, 1895.] 



KNOWLEDGE. 



165 



chemical processes, after ascertaining the ingredients in 

 tlie irnmuuized blood-serum, that the people of India must 

 look for the proper antidote in cases of snake poisoning. 

 There would be suflicient time to administer the anti- 

 venine, as death does not ensue until from three to 

 twenty-four hours after a bite. 



At the close Trof. Rutherford, the celebrated physiologist 

 and experimentalist, stated that he had never listened to 

 such a lucid account of a series of experiments, and he 

 was very glad that it was in Edinburgh University that 

 such a valuable discovery had been made. 



ORGANIC MATTER AND WATER FILTERS. 



DR. S. RIDEAL recently discussed in Knowledcje 

 the objects and methods of the filtration of large 

 waterworks. As he pointed out, it is now clearly 

 known that the capacity of water to cavise disease 

 depends directly, not on its chemical but on its 

 bacterial contents. The danger of pathogenic organisms 

 lies essentially in the enormous rapidity with which they 

 grow under favourable conditions. The circumstances in 

 the composition of water which assist or repress the 

 growth of organisms have not yet been definitely worked 

 out ; but it is certain that temperature, bacterial and even 

 mechanical contents, and chemical composition have a 

 more or less defined influence. Accordingly, in the criticism 

 of a supply proposed for a large town, chemical analysis is 

 a factor of which account must be taken, and as more 

 definite results are obtained connecting variations of 

 chemical composition with alterations in the capacity of 

 an organism to develop, such analysis will for this purpose 

 have an increasing value. In the case, however, of domestic 

 filters, the importance of chemical analysis becomes con- 

 siderably less, as the water will be kept for a relatively 

 short time after filtration, and the increase of organisms, 

 either through their growth in transit or through the 

 accidental pollution of the supply in the pipes, will already 

 have taken place. In the examination of a domestic 

 or industrial water filter, it is therefore usually im- 

 material to determine whether or not any chemical altera- 

 tion has occurred in the water during filtration. This cir- 

 cumstance to some extent simplifies the task of examining 

 the water filter, but entails the necessity of entirely recon- 

 sidering the data which hitherto have been taken as relevant 

 in the construction of such filters. Formany years before any 

 positive connection was established between typhoid fever 

 and a specific micro-organism, it was established that this 

 and other diseases were in some way connected with the 

 composition of the drinking water previously consumed by 

 the patient. By chemical analysis it was found that in 

 almost all cases of such diseases the water contained an 

 excess of organic matter, and when a water supply with 

 less organic matter was substituted for that which had 

 been connected with an epidemic, the disease invariably 

 disappeared. It was accordingly considered a reasonable 

 inference to regard the organic matter as being at the root 

 of the disease, and its removal as a sufficient sanitary 

 precaution. The presence of excess of organic matter in 

 dangerous waters was due to the larger capacity of such 

 substances to support the life and favour the growth of the 

 specific micro-organisms, and the filters, still largely in use, 

 which arrested such organic matter are thus seen to 

 furnish a culture-bed of concentrated nutrient value for 

 such disease organisms as may occur in the water. 

 Accordingly, when such a filter ia tested with polluted 

 water for a few days, it is found that the filtrate is much 

 richer in micro -ovganisms than the nntiltered water. If 



subsequently sterile water be passed through it, the 

 filtrate may come out teeming with microbes. At the 

 same time such filters are, in fact, found to be incapable 

 of preventing the direct passage of micro-organisms, and 

 accordingly, both by permitting them to pass directly into 

 the filtrate and by multiplying those which are retained, 

 they are now known to be dangerous to health. 



These facts have recently been verified by examinations 

 of all known types of filters by Dr. Sims Woodhead and 

 Dr. Wood, at the Research Laboratory of the Colleges 

 of Physicians and Surgeons, and by a very minute 

 examination of representative filters made at the Public 

 Health Laboratory of the University of Edinburgh by 

 Dr. .Johnston. These researches confirm entirely earlier 

 results obtained by Continental investigators, beginning 

 with M. Pasteur, who in 1878 stated to the Academy of 

 Sciences that no material had yet been discovered capable 

 of arresting micro-organisms. There can be no question 

 but that such results have demonstrated conclusively the 

 worthlessness and the danger of the filters which they 

 condemn. It is doubtful whether any practicable labora- 

 tory experiment can, in the present state of knowledge, 

 warrant the eSiciency of a filter ; the difficulty being that, 

 in the absence of a definite relation established between 

 the composition of water and the source of organisms on 

 the one hand, and the conditions favourable to the develop- 

 ment of organisms which apparently are necessary for an 

 epidemic on the other, it is almost impossible to be certain 

 of reproducing in laboratory examination the conditions 

 which occur in actual practice during epidemics. Prob- 

 ably, therefore, the course which for the present must be 

 taken in the examination of water filters proposed as 

 sufficient for the prevention of water-borne disease, is to 

 simultaneously examine them under identical conditions 

 with some filter of which the efficiency has been indepen- 

 dently established. Up to now the only filter in regard 

 to which adequate practical evidence is available is that 

 of Pasteur. It was applied some seven or eight years ago 

 to those quarters in the French army in France, Algeria, 

 Tunis, etc., where the water supply was most polluted or 

 suspicious, and the civil population were subject to 

 endemic or epidemic typhoid fever. The total number of 

 quarters so fitted is 24.5,000. The results of the applica- 

 tion of this filter are necessarily derived from a very large 

 number of independent health returns, which are only 

 collated at head-quarters, and therefore cannot be vitiated 

 by personal bias or error. The area over which the 

 experiment, if it may be so called, was conducted includes 

 so large a variety of climate and water conditions, and the 

 period of observation was so long, that any result common 

 to the whole of the installations may be stated in general 

 terms as characteristic of the appliances ; while the 

 constant presence of a civil population not furnished with 

 the filters would have constituted a current control- 

 experiment, by which the results of coincidence could at 

 once be eliminated, even if the scale of the observations, 

 both in point of number and of extent in time, had been 

 insufficient to do so. In other words, the experience 

 derived from this enormous use of a single type of appli- 

 ance, in the circumstances disclosed, gives a reliable basis 

 for a strict induction. The result of the experiments is 

 expressed in the reports of M. de Freycinet while Minister 

 of War from 1889 to 1892, in which, after tracing a con- 

 tinuous decrease of typhoid fever in every year, he finally 

 reports that in every case where the Pasteur filter had 

 been applied, even in districts previously the most at- 

 tacked, typhoid fever had disappeared. General /urlinden, 

 the present Minister of War, published in April a further 

 rej)nrt on tlif «a.mp siihject, not onlv 'iVinwing an incren,!??*^ 



