1893.] MICROSCOPICAL JOURNAL. 139 



of stucivin*^ tlic microscopical life is anotliLT step which bids fair 

 to advance our accurate kiKJwletlj^e of the sanitary relations of 

 potable water as much or even more than a knowleilj^e of the bac- 

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

 liberal policy of the Massachusetts State Hoartl 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 bein<js is unsafe for domestic use for a lon<; 

 time thereafter. 



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

 beinpjs, 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 luuiian lieings. 



(S) The self-puriHcation of a stream, pf)n(l. or lake receiving 

 sewage may proceed from (a) the ciiemical force of oxidation; 

 (/>) 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 likelv to be a source of grave dan- 

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

 reproduce themselves iiidctinitelv. 



(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 tvphoid 

 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 immimity 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 upon to reduce somew hat the danger of pollution. 



(11) Filtration will also improve the qualitv 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. i^ and 16. A 

 large attendance is hoped for. 



