32 IOWA ACADEMY OF SCIENCES. 



Various bacteriologrical analyses made in Europe and the United States show that 

 the bacterial contents differ greatly. Dr. Grubei'^ sets the maximum number of 

 colonies to be found in spring: water from 40 to 50, in well water 300 to 500 per c. c. 

 Fraenkel states that g:ood drinking water should not have more than fifty g^erms per 

 cubic centimeter. Many bacteriologists place the limit at 1,000 germs per c. c. 

 It is stated that water taken from the Croton reservoir. New York, contained from 

 5,000 to 15,000 germs per c. c, and Messrs. McCall and Patton found in well water 

 from a well near the Iowa Agricultural College, 320 germs per c. c. Spring college 

 water supply only contained 56 germs per c. c. Water taken from the Muenich 

 supply contained from 305 to 12,606 germs per c. c. FrsenkeF estimated the num- 

 ber of germs in the water supply of Berlin at 6,140, while below the city there was 

 a great increase, the number being 243,000 per c. c. The Kiel water supply, 

 according to Breuning*"*, has from 62 to 1,712 germs per .5 c. c, the number of 

 liquefying species varying from 4 to 188. Wells in the same city in some cases had 

 more than 26,000. 



Sewage, of course, contains an enormous number. Out of 126 analyses of Law- 

 rence sewage, the number was 708,000 per c. c; the minimum was 102,400; and 

 maximum, 3,963,000. Fourteen analyses show more than 1,000,000 per c. c. It is 

 not strange that sewage should contain such large number?, since the putrefying 

 material is especially favorable for their development. Nor is it strange that well 

 water should often contain large numbers, since the upper strata of the soil teem 

 with bacteria, and it is especially easy for water from the surface to find its way 

 into the well. In bacteriological analysis of water it is not so important to deter- 

 mine the number as it is the quality of the germ. It is of special importance to 

 take into account the pathogenic organisms, like the typhoid fever bacillus, and 

 the spirillum of Asiatic cholera, in cases of epidemics of the latter disease. The 

 liquefying species, such as peptonize gelatin, are more important than those which 

 do not, since many of these give rise to very disagreeable odors, and perhaps poi" 

 sonous products. What becomes of the germs found in sewage? It is certainly 

 important to know whether they will continue to contaminate cities using the 

 same water and lying farther down the stream. 



Water may be purified in two ways: 1. Self-purification; 2. Purification by fil- 

 tration. In this paper we are only concerned in the first. Destruction by various 

 small animals, chemical action, sedimentation, and direct sunlight. The chemical 

 action is perhaps due largely to oxidation; the mechanical effects of the small par- 

 ticles m the water must act to a considerable degree on the germs; the sediment 

 carries with it much organic matter; this sediment, as experiments have shown, 

 contain pathogenic germs. Perhaps the most powerful agent is sunlight. Buch- 

 ner,8^ Marshall Ward, and others, have shown that exposure of typhoid bacillus, 

 anthrax and other germs to direct sunlight destroys their pathogenic properties 

 and inhibits their growth very materially. That there is a constant decrease in the 

 number of germs at some distance below the point whei-e sewage empties into the 

 stream, numerous analyses have shown. 



"SSehrank. Anleitung zur Ausfuehrung bacteriologischer Untersuchungeu zum 

 Gebrauche fur Aerzte, Thieraerzte, Nahturungsmittel— , Agricultur and Gaehrungs- 

 chemiker, Apotheker and Bautechniker, pp. 255, with 137 figures. Leipzig and Vieuna. 

 Franz Denhicke, 1894. 



801. c. p. 820. 



soaBacteriologischeUntersuchung desTrinkwassersderStadt Kiel im August und 

 September, 1887. Inaugural Diss., pp. 38. Kiel, A. F. .Jensen. 



siBot. CentralDlatt Vol. LII., pp. 61, 398. 



