138 THE AMERICAN MONTHLY [May, 



tains vast numbers of more or less perfectly recognizable frag- 

 ments of muscle derived from the meat eaten as food. The frag- 

 ments are not in the condition of cooked meat, but are so modified 

 by the digestive process as to be no longer soluble in a warm 

 acid solution of pepsin. They are also insoluble in a dilute warm 

 solution of caustic potash. Again, they resist decomposition for 

 a far longer time than cooked meat, when kept in water ; at the 

 same time showing the microscopical structure of muscle with 

 such marvellous perfection that they cannot be confounded with 

 any other object. 



(3) Human fteces vary in composition according to the food 

 eaten. Green vegetables furnish many spiral vessels, while fteces 

 from oatmeal abound in the hairs of oats. 



(4) Horse excrements play the most important part in street 

 washings. Their most characteristic objects are hairs of oats and 

 spiral vessels derived from straw or green fodder. 



(5) It is quite witliin the possibilities of our present knowl- 

 edge to prepare a microscopical scale of comparison bv the use 

 of which to estimate the amount of sewage contamination in any 

 given sample of water. 



The foregoing discussion presents a few of the points to be 

 taken into account in determining the various circumstances affect- 

 ing the quality of a public water supply. Without pretending to 

 legitimately make all the deductions from this inadequate pres- 

 entation of some of the elements of the subject, we may still lay 

 the following down as practical points to be borne in mind when 

 studying questions of sanitation in relation to public water sup- 

 plies, namely : 



(i) The circumstances affecting the quality of a public water 

 supply are of an exceedingly complex nature. So true is this- 

 that what appears to be a cause of disease at one time may pos- 

 sibly become under different conditions the source of immunity 

 from danger. Hence a knowledge of the detail is indispensable 

 for a really rational decision in nearly every case. 



(2) The most complete system of chemical study thus far de- 

 vised is the combustion method of Dr. Frankland, but the diffi- 

 culty of working it has prevented its general adoption in actual 

 work. At the present time, by reason of the perfection of the 

 systems of biological examination, the simpler albuminoid am- 

 monia process of Wanklyn answers all the requirements of the 

 purely chemical study. 



(3) Dr. Frankland's method of estimating the previous sew- 

 age or animal contamination is interesting as showing how com- 

 pletely he realized, twenty years ago, the value of more definite 

 information about the natural history of water. 



(4) The working out of exact methods of studying the bac- 

 teria about ten years ago was a great step in advance in determin- 

 ing the sanitary relations of potable water. 



(5) The working out in the last three years of exact methods 



