50 LOGARITHMIC ORDER OF DEATH 



production, is due to the lethal inactivation of some geue, 

 this must apply not only to bacteria, but to all other 

 unicellular beings as well, at least as long as they are mo- 

 nonucleate. That the order of death of yeast is logarith- 

 mic has been shown by Woerz (Fig. 11), by Rahn and 

 Barnes (1933) and especially by Beamer and Tanner 

 (1939b). Some of the data obtained by the last mentioned 

 authors are given in Fig. 2 and Table 7. Since certain 

 species of yeast have a tendency to form cell aggregates 

 in consequence of the fact that the daughter cells, and 

 even the third generations, frequently remain attached to 

 the mother cells, the survivor curves may eventually be- 

 come concave downwards (Eijkman, 1912). Beamer and 

 Tanner avoided clumps by shaking their stock cultures 

 for 30 minutes and filtering them through cotton before 

 exposure. 



The survivor curves of mold spores, whether death is 

 caused by heat or by disinfectants, are concave down- 

 wards (Henderson Smith, 1921 and 1923). Although mul- 

 tinuclear, the spores could not develop, or would at least 

 become abnormal, if one of the nuclei were inactivated. 

 On that basis one would expect a logarithmic order of 

 death. But it is probable that spores are fairly resistant 

 in their natural dry state, and the penetration of water 

 is known to be a slow process requiring considerable 

 time. Germination is often irregular. Fig. 12 shows 

 the rate of germination of the spores of Aspergillus niger 

 on an agar surface. The percentage of germination was 

 ascertained every 10 minutes, and the mold spores were 

 found to be very inhomogeneous. Since germination as 

 well as disinfection depends above all upon the penetra- 

 tion of water, such material cannot be expected to show a 

 constant death rate. However, X-rays should cause a 

 logarithmic order since they penetrate instantaneously. 



