78 ILLINOIS ACADEMY OF SCIENCE 



water at one time to obtain a medicinal dose of 2 milligrams. 

 From this it is readily seen that the arsenic content of filter 

 alums used in Illinois is of no significance. 



All alums used in this State are supplied by western manu- 

 facturers. Several samples have been obtained from the East. 

 In some of these the arsenic content is much higher than that 

 of the Illinois alums. This matter is being investigated fur- 

 ther and will be reported later. 



THE LONGEVITY OF BACILLUS COLI AND 

 BACILLUS TYPHOSUS IN WATER 



M. E. HINDS, UNIVERSITY OF ILLINOIS 



It has long been known that in natural water there is a ten- 

 dency of the intestinal bacteria to die out, but very little is 

 known concerning the conditions which govern their death 

 rate. The available data on the subject deal mostly with streams 

 and reservoirs and are influenced by several variable conditions. 

 Very few data are to be found dealing with pure cultures of 

 bacteria and with known conditions of light, temperature, food 

 supply, dissolved oxygen and the presence or absence of other 

 micro organisms. 



Most of the published data on the death rate of bacteria 

 refer to death by drying or by disinfectants. The best work 

 has been by Madsen and Nyman 1 , Paul', Harriett Chick', 

 and Eijkman 4 . Their results show a constant rate of death. 

 When the logarithms of the number of bacteria present are 

 plotted against the time, a fairly straight line results. This is 

 the curve of the monomolecular law and was first noted by 

 Madsen and Nyman and lated used by Harriett Chick, who 

 determined constants for all of her data. 



All of our work was done with pure cultures of B. Coli and 

 B. typhosus, kept constantly fresh and vigorous by daily trans- 

 fers in one per cent lactose broth. When the culture was to 

 be used, smears were made on agar plates and grown for 12 

 hours, then suspended in sterile water and suitable portions 

 of the suspension used. This method is better than that of 

 using broth cultures for inoculation as only a minimum amount 



1. Madsen and Nyman. Beit. f. Hyg. 57, 388, 1907. 



2. Paul. Biochem. Zeit., 29, 202 and 249, 1910. 



3. Chick. Jour, of Hygiene, 10, 237, 1910. 



4. Eijkman, Verslag. der kon. Akad. Wetenschaffen, V. 21, 1, 510, 1912. 



