378 



PHYSIOLOGY OF BACTERIA 



the average of 5 to 6 experiments. The bacteria had been grown at 

 37° for twelve hours before being placed in the water. At 8°C., the 

 death rate was very high during the first six hours, at 20°C., not 

 quite so high, and only for two hours, while there is nothing abnormal 

 at all at 37°C. The numbers in brackets are not averages; each 

 represents but one single datum. The very high death rate for the 

 first few hours, which was observed only at low temperatures, is 

 very probably due to cold-shock. Those cells which survived the 

 cold-shock died more slowly from starvation. 



Table 120. — Relative Death Rates of Bad. coli and BacL 



typhosum in Water 



(Standardized to the average = 100) 



A typical starvation experiment is the following by- 

 Rogers (1918) which shows a rapid decline of bacteria 

 in sewage if dialized in running water, after the first 

 day. Here, we see plainly the short induction period 

 due to reserve food materials in the cells, and the increas- 

 ing death rate. 



Quite extensive experiments were carried out by Cohen 

 (1922) who studied the death of Bad. typhosum and of 



