136 THE AMERICAN MONTHLY [May, 



This remark is especially true in case sewage contamination is 

 present. 



And this brings us to another point ot great practical importance, 

 namely, as to the possibility of definiteU' determining by the mi- 

 ci'oscope whether or not sewage contamination is actually pres- 

 ent in a given sample of water. For a long time the matter of 

 sewage contamination has been a stumbling-block in the way of 

 satisfactory interpretation of the results of chemical analysis. We 

 have already seen the cumbersome methods of expressing the 

 fact of sewage contamination resorted to by Dr. Frankland in his 

 combustion process, and we may further remark that the exten- 

 sive application of this method made to polluted river water by 

 Dr. Frankland has been the cause chieflv of the adoption of what 

 must be considered an unnecessarily high standard of purity in 

 the case of streams from which a study of the environment shows 

 sewage contamination to be absent. In the same way Wanklyn, 

 working largely upon sewage-polluted London wells, fixed upon 

 an arbitrary standard, which, while properly applicable to such 

 wells, is little worth when applied to streams and surface 

 waters generally.* 



At the present time it may be affirmed that in the case of sur- 

 face waters the microscope will usually show evidence of sewage 

 contamination when such exists. The cases in which it mav not 

 furnish definite evidence are those in which, by reason of the water 

 flowing considerable distances, sedimentation has been sufficiently 

 thorough to remove the kind of evidence which the microscope 

 is fitted to detect. Even when this has occurred an examination 

 of the deposit of mud at the bottom will easily lead to the detec- 

 tion of the specific constituents of sewage. This part of our sub- 

 ject, although capable of yielding practical results of the very high- 

 est value, is nevertheless, with the exception of a small amount of 

 work in Germany and England, as yet almost entirely undevel- 

 oped. 



The beginning of the use of the microscope for detecting sew- 

 age contamination in potable water dates from the researches of 

 Prof Nothnagel, who published, about fifteen years ago, the re- 

 sults of an investigation into what mav be termed the fixed con- 

 stituents of human excrements. Prof. Nothnagel found that there 

 were four substances of almost constant occurrence in fiecal mat- 

 ter, namelv, muscular tissue, yellow elastic tissue fibre, shreds of 

 fibrous substances, sucli as fasciae, and finally spiral and free veg- 

 etable cells. All of these are so far capable of resisting the action 

 of the digestive fluids that they pass away in the faecal matter 

 either in an unchanged or so far unchanged state that they may 



* On the necessity for varying chemical standards for different classes of water, see a Pre- 

 liminary Report of a Chemical Investigation into the Present and Proposed Future Water 

 Supply of Philadelphia, by Albert R. Leeds, Ph. D., in An. Rept. Phil. Water Dept., 1883, 



P-243- 



Also see The Odor and Color of Surface Waters, by Thomas M. Drown, M. D., Prof, of 

 Analytical Chemistry in the Massachusetts Institute of Technology, etc., in Jour. New. Eng. 

 W \V. Assn. for Mch., 1888, pp. 2-29. 



