28 Ciuciumxli Society of Natural History. 



unpleasant taste — though we know there are differences in 

 taste between specimens of water that are equally harmless, 

 or healthy. There is no precision in a standard established 

 l)y such imperfect tests; as far as they go they have a value. 



The next method in hi.storical .sequence is the chemical one. 

 vSimple as water is in its constituent elements, its chemical 

 analysis was always difficult by reascni of the amount of for- 

 eign ingredients, which its solvent ])owers enabled it to hold. 

 There must be wondrous skill in nature's laljoratories, when 

 we see waters issuing from thousands of springs that are !-:o 

 varied, subtle, .selective, constructive and constant in their 

 ingredients. At that time they are pure, and scarcely not one 

 of them contains an ingredient that will prove acutely toxic 

 to the consumer. The potentiality of ])oison begins after- 

 ward, and, as we shall see, usually after man has impressed 

 them into his service. 



The chemical standard admits of great precision, though 

 variations are found. The u.sual saline ingredients are not 

 nece.ssarily hurtful, they are often helpful in nutrition. After 

 all of the amount of chemical work applied to the determina- 

 tion of a .standpoint of purity, the most important ingredient, 

 so far as disease is concerned, is the organic matter. Chemis- 

 try can not sa}' exactly what is a harmful amount. It will 

 give some help in ascertaining its origin, as, for instance, in 

 sewage contamination. Perhaps, in this countrj', the best work 

 of this kind in our country has been done in Massachusetts, 

 under the auspices of the vState H(jard of lieallh. Dr. W'al- 

 cott''- of that Hoard states that their e.xamiuations ha\e shown 

 that the amount of chlorine may be assumed as the standard, 

 "That it survives all the changes" that mixtures of sewage 

 and water undergo. The\' liave constructed a chart, which 

 shows all the sources of etpial amounts of chlorine, which, 

 being connected as isobars on weather maps, are called 

 " Isochlors." When a water brought in for analysis shows an 

 amount of chlorine greater than that designated by the 

 " Isochlor" of that locality, the presumption of pollution b\ 

 sewage, more or le.ss remote, is seldom a mistake. This is as 

 simple a standard as we know of. 



After all, our most conclusive knowledge as to the relations 



'-'.\B80ciation Aiiierican I'liysicians. VqI. h, p. 222. 



