ON BACTERIOLOGY IN ITS RELATIONS TO CHEMICAL SCIENCE, 455 



chemists. Thus the investigation of numerous hygienic questions, more 

 especially relating to water supply and sewage disposal, forms a very 

 important part of professional chemistry, and the bearing of recent 

 bacteriological research on these questions must of necessity, therefore, 

 be of peculiar interest to many chemists. When the bacteriological 

 examination of water first came into vogue some eight or nine years ago 

 there was a general impression amongst enthusiasts for the new science 

 that it would, in a very short time, entirely supersede the chemical ex- 

 amination owing to the inability of the latter to distinguish between dead 

 and living organic matter, and to reveal the presence of disease-producing 

 organisms. From the newly established bacteriological laboratories 

 on the Continent there emanated in rapid succession publications in 

 which standards of bacteriological purity for water were hastily set up 

 by men who, whilst doubtless very skilful bacteriologists, were quite 

 ignorant of the subject of water supply, with its numerous complicating 

 factors. It is quite unnecessary for me to enter into a discussion of these 

 standards of purity, because happily they have been banished from the 

 vocabulary of those who have had any considerable experience in these 

 matters. 



Many persons, again, have been, and are still, under the impression 

 that the main object of an examination of water is to ascertain whether 

 it contains materials capable of causing disease, and that the inability of 

 chemical analysis to answer this question proves its inutility. The 

 absurdity of this view is so manifest, and the misconception to which it 

 is due so obvious, that its wide prevalence is my only excuse for referring 

 to it. A water examination which only reveals the unsuitability of the 

 water when disease germs are actually present in it can surely be of 

 little value indeed, inasmuch as the mischief will in all probability have 

 been already done before the examination has been made or thought of. 

 The object of a water examination should obviously be to ascertain 

 whether a water is liable to be a source of danger, and not whether it 

 is actually dangerous at the moment of examination. Now I have no 

 hesitation in saying, and I have frequently expressed it as my opinion 

 during this controversy, that a proper chemical analysis is able to throw 

 more important light on this question than a bacteriological examination. 



On the other hand, I have from the very first turned to bacteriology 

 for an answer to some questions concerning the hygienic aspects of water, 

 which I am equally strongly of opinion cannot be answered by chemical 

 methods of examination at all. Already in 1885 I pointed out in a paper 

 to the Royal Society, ' On the Removal of Micro-organisms from Water,' 

 and elsewhere how the then recently introduced methods of bacterio- 

 logical research enabled us for the first time to ascertain the real hygienic 

 value of methods of water purification, both artificial and natural, such as 

 sand filtration, subsidence, precipitation as in Clark's process, natural 

 filtration through porous strata, &c. 



Thns I showed that the improvements effected in the quality of water 

 by sand filtration, by Clark's process, and by subsidence are quite insig- 

 nificant — from a chemical point of view — as compared with their bacterio- 

 logical eflBciency. The bacteriological effect of these processes may be 

 illustrated by means of the following tables summarising some of my 

 results. 



Thus the first two tables show the remarkable efficiency of sand- 

 filtration in removing micro-organisms from water: — 



