32 LOGARJTHMIC ORDER OF DEATH 



curves that he considers sigmoid. Six of the experi- 

 ments required 180 minutes ; the shortest one lasted 52 

 minutes. This represents a slow death for disinfection 

 experiments. It will be shown on p. 48 that a sigmoid 

 survivor curve must be expected when death is so slow 

 that repair becomes appreciable. 



After the first few minutes, Knaysi's curves are shaped 

 quite differently from any survivor curves for higher 

 organisms (plotted on semi-logarithmic scale). Five are 

 concave upwards, indicating inhomogeneous material 

 (probably due to the use of cells from agar cultures in- 

 stead of from the customary liquid cultures), two are 

 straight, and three are so irregular that they would not 

 fit any theory. Knaysi concluded that "these results 

 can be adequately explained only if the distribution of 

 resistance in cultures of bacteria is considered to govern 

 the course of the process." 



Knaysi later (paper V) approached the problem math- 

 ematically by using Pearson's curves of variability. The 

 curves shown in his graphs are quite ditferent from any 

 mortality curves known for higher organisms. He fur- 

 ther quotes Yule who "demonstrated that if the cells are 

 to be considered all alike, and if the action of poison is 

 noncumulative, the law of chance gives an exponential sur- 

 vivors ' curve. If the action is cumulative, the death rate 

 constantly increases." However, in Knaysi's experi- 

 ments, the death rate increases only for a few minutes 

 and then declines rapidly. 



But the main point of the controversy is the shape 

 of the mortality curves during the very first minutes of 

 exposure. The determination of this shape is practi- 

 cally impossible because one cannot prove that, with 

 bacteria, death begins at the moment of exposure, and 

 because one can always argue that the bacteria which 

 were found dead after the first minute, all died in the 

 second half of this minute. Even for the x-ray experi- 

 ment of Figure 8 where the first observation was made 



