MECHANISM OF DEATH 369 



With HgCl2, the formation of mercury-proteinate 

 does not seem to be the cause of death, but only of dor- 

 mancy, because the administration of H2S as antidote 

 brings the cells back to life unless the dormancy has 

 been very prolonged. 



The death rate is sometimes proportional to the 

 concentration, but more commonly, it is proportional 

 to the nth power of the concentration where n is known 

 to vary from 0.5 to 4 or even 6. This means that the 

 relative strength of two different disinfectants cannot 

 be expressed by a simple factor unless the comparison 

 is limited to a definite range of concentration, or, as in 

 the case of the Rideal-Walker method, to only one 

 definite killing time. No better method has as yet been 

 found to compare disinfectants. 



For low concentrations, the exponent becomes larger. 

 At very low concentrations, the toxic effect disappears 

 entirely, and a stimulation is frequently observed. 



The temperature coefficient of disinfection shows 

 some queer anomalies. It increases with an increasing 

 concentration of bacteria, and it is higher with young 

 cells than with old ones, but as a rule, is normal, or 

 only slightly above normal. 



VIII. DEATH BY SURFACE TENSION DEPRESSION 



The theory that all death by chemical poisoning is 

 caused by surface tension depression has already been 

 discussed on p. 366 and found to be an unsupported 

 generalization. However, in solutions of very low 

 surface tension, death is probably brought about 

 primarily by physical rather than chemical causes. 



The first experiments of Ayers, Rupp and Johnson 

 (1923) showed no parallelism between surface tension 

 and death rate. These authors, therefore, considered 



