242 The Future Water-supphj of London. [April, 



tion, so the organic nitrogen may be made an index to the p-esent 

 sewage-contamination, on the same assumption as before, namely, 

 that one part of nitrogen corresponds to 10,000 of sewage. 



With regard to the presence of organized germs, such as cholrads 

 in the water, their chemical composition would probably approxi- 

 mate to that of albumen; but theu' minute size, as it has hitherto 

 rendered it impossible to detect them in water by the microscope, so 

 it serves to place them beyond the reach of chemical methods. Even 

 if we could distinctly prove the presence of albuminoid compounds 

 in a sample of water, it would, on chemical evidence, be impossible 

 to say whether or not it was organized. It might consist of white of 

 egg, or it might consist of cholrads, for anything that an analysis 

 could show. The only safeguard which can be adopted against 

 the presence of noxious germs in our drinking-water is, as I have 

 ah-eady said, the complete exclusion of all sewage from sources of 

 the supply. 



Although the microscope has hitherto failed to detect in water 

 the germs of zymotic disease, it must not be supposed that its 

 indications are of no value in the diagnosis. When Dr. Hassall 

 was preparing his Eeport to the Committee, which, in 1854, was 

 commissioned by the Medical Council of the General Board of 

 Health to make scientific inquiries in relation to the cholera 

 epidemic of that year, he observed and described a great many low 

 forms of Kfe in the waters consumed in London. Some of the 

 animal forms are terrible -looking monsters, and the coloured draw- 

 ings in which they are portrayed are by no means pleasant to 

 contemplate.* But Dr. Hassall states exphcitly that none of these 

 tiny monsters can be identified in any way with the cholera, for all of 

 them are found frequently when cholera is absent. In like manner 

 he found vibrions in myriads in " every drop of every sample'' of 

 the rice-water discharges of cholera patients which he examined; 

 but knowing the ease with which vibrions are developed under a 

 variety of circumstances, he did not venture to connect them in a 

 causal relation with the disease. But we must remember that 

 animalculae are formed of albuminoid compounds, and that if their 

 germs develop in the water, it is a certain proof that the nourish- 

 ment necessary for their subsistence is present. In pure water it is 

 impossible for organic life to be developed ; and the presence of such 

 life may therefore be taken as a certain proof of nitrogenous and 

 therefore probably of sewage contamination. In fact, I cannot help 

 agreeing with Dr. Angus Smith, in the belief that the microscope is 

 too much neglected in examinations of water. 



The length to which this article has already extended has left 

 me but little space fur a consideration of the various projects for the 

 amelioration of the water-supply of London which are now before 



* Fee, for oxni.iplc, Plates 5, 10, and 12, in Appendix to Report. 



