286 PHYSIOLOGY OF BACTERIA 



9% of the original number of cells will again become 

 sterile, unable to multiply, and only 1% of the original 

 cells is left unchanged. After the third minute, only 

 0.1% of all cells will be able to grow, and so on. This 

 order of death is identical with that of a monomolecular 

 reaction (see p. 278). 



For chemical reasons, then, uniform cells cannot all die 

 at the same time, but must follow the mass law. If the 

 cells are not uniform, the order of death is different, as 

 shall be shown presently. This order of death does 

 not apply to death by physical causes (e.g., freezing). 

 There are some other exceptions, e.g., death by starva- 

 tion. Why the effect of poisons must be considered 

 monomolecular, will be explained on p. 341. 



From this one extreme, where the inactivation of only 

 one single molecule causes death, to the other extreme 

 of the higher organisms, where many cells must be 

 inactivated before the organism dies, there are many 

 intermediate steps. Rahn (1929c) computed a general 

 formula for the order of death for any number of '^react- 

 ing molecules," i.e., molecules which have to be changed 

 to bring about death. Figure 32 gives the logarithms of 

 survivors plotted against time. It shows a straight 

 line only for one reacting molecule. For all other cases, 

 the line is not straight, but shows at first a period of no 

 deaths, and then turns sharply down in a curve which 

 is not really straight, but might be mistaken as such. 



Rahn found (1931a) that death of Colpidium by 

 HgCl2 seems to be brought about by the reaction of two 

 molecules per cell, and that avian red blood corpuscles 

 when exposed to ultraviolet light, also dissolve after the 

 inactivation of two special molecules. With yeast, death 

 was brought about sometimes by one, sometimes by 

 two inactivated molecules. Mold spores seem to con- 



