LOGARITHMIC ORDER OF DEATH 



51 



Fig. 12. Irregularity in the number of spores of Aspergillus which 

 germinate per time unit (on an agar surface). Abscissa: time from 

 the moistening of the spores; ordinate: per cent of germinating spores. 



The order of death of algae has been studied occasion- 

 ally. Harvey (1909) found a logarithmic order when 

 Chlamydomonas was treated with hydrochloric acid (Fig. 

 13). The criterion was the loss of motility. 



With protozoa, the same criterion resulted in a sur- 

 vivor curve which was pronouncedly concave down- 

 wards. Peters (1920) studied death in the flagellate Col- 

 pidium in dilute solutions of Hg Cl> ; the survivor curve 

 he obtained is shown in Figure 14. It is possible, of course, 

 that loss of motility is one of the latest symptoms to be- 

 come noticeable, and that the protozoa were doomed to 

 die before this criterion could be observed. 



Unexplained Deviations from the 

 Logarithmic Order. The evidence on hand is 

 overwhelmingly in favor of logarithmic order of death in 

 bacteria, and isolated reports of exceptions could be dis- 

 regarded. However, there are some consistant excep- 

 tions which cannot be disregarded although they are un- 

 explained. The following two very extensive sets of ex- 

 periments on disinfection by chlorine, carried out inde- 



