1893.] MICROSCOPICAL JOURNAL. 139 



of studying the microscopical lite is another step which bids fair 

 to advance our accurate knowledge of the sanitary relations of 

 potable water as much or even more than a knowledge of the bac- 

 teria. For this latter advance we are chiefly indebted to the 

 liberal policy of the Massachusetts State Board of Health. 



(6) At the present time all studies point to the conclusion 

 that a water once polluted with the excrements of either domestic 

 animals or human beings is unsafe for domestic use for a long 

 time thereafter. 



(7) As between the pollution of domestic animals or human 

 beings, the weight of recent evidence is, other things being 

 equal, that the pollution from animals is the source of the greater 

 danger, for the reason that intercommunicable infectious diseases 

 are more virulent when communicated from animals to men than 

 from men to animals. It is found, too, that domestic animals are 

 quite as liable to infectious diseases as are human beings. 



(8) The self-purification of a stream, pond, or lake receiving 

 sewage mav proceed from (a) the chemical force of oxidation; 

 (6) the biological force of reduction of organic matter to harm- 

 less forms through the medium of life processes, and (c) sedi- 

 mentation. An apparent self-purification may also be attained 

 by mere dilution. In regard to oxidation and biological reduc- 

 tion, the difficulty at present is to determine when they are com- 

 plete ; while sedimentation is likely to be a source of grave dan- 

 ger bv reason of furnishing a field in which disease germs may 

 reproduce themselves indefinitely. 



(9) It is clear from the preceding that running streams which 

 receive sewage may be unsafe sources of water supplies for many 

 miles below' the point of inflow. Incidentally it may be re- 

 marked that the recent investigations in relation to the typhoid 

 germ which have been made in Massachusetts and other places 

 have enforced this point in another way, which need not be specially 

 referred to at this time. 



(10) Absolute immunity can be obtained by drawing water 

 supplies from areas entirely free from animal pollution of every 

 sort and kind. When this is impracticable intelligent supervision 

 may be relied iipon to reduce somewhat the danger of pollution. 



(11) Filtration will also improve the quality of polluted water 

 supplies. 



(12) — As a fair practical summation of the whole matter, we 

 may say, in conclusion, that the water-works manager of the 

 present day, in addition to being a business man and a working 

 engineer, needs to be something of a chemist and biologist as well, 

 to this extent, that he may be able to quickly appreciate all the 

 circumstances affecting the quality of a public water supply. 



American Microscopical Society. — The meeting for this 

 year will be held at Madison, Wis., August 14, 15 and 16. A 

 large attendance is hoped for. 



