32 Killing of Botrytis Spores by Phenol 



inoiiient is strictly proportional to the number alive at that moment. 

 These workers do not as a matter of fact always obtain curves of this 

 type — many of their results indeed depart very widely from it. But 

 the logarithmic type is held to be the true one, and the departures from 

 it to be variations caused by factors independent of the disinfection 

 process itself. The sigmoid shape of curve is, on the other hand, a type 

 occurring with great frequency in biological investigations of this kind. 

 The hterature of haemolysis is full of examples of it. Even with bacteria 

 some workers find curves of this type occurring with heat or chemical 

 poisons, and some of the experiments with staphylococci recorded by 

 Chick would seem to fit a sigmoid curve as reasonably as a logarithmic 

 one. It occurs also with more highly developed organisms, e.g. it was 

 obtained by Boycott in the kilhng of tadpoles by hot water (6). A good 

 example may be seen in a recently pubhshed paper on the habits of 

 the Tomato Moth (7), where the poison used was a lead arsenate paste. 

 The plants were sprayed with a suspension of the paste, and then in- 

 fected with the larvae of the tomato moth. On successive days there- 

 after the survivors were counted, and the results are tabulated. It is 

 found that the larvae die off gradually, some being dead the day after 

 the spraying, others surviving a week or more. The explanation offered 

 is that the larvae find the paste distasteful, and the majority cease 

 feeding before they have taken a fatal dose. After a time hunger forces 

 them to recommence feeding, until finally a fatal dose is absorbed by 

 all. The death-rate, however, is probably an example of the same 

 phenomenon as that described above. I have plotted the figures given 

 by Lloyd and reproduce in curve form two of his experiments (see 

 Fig. 2). The sigmoid curve is well illustrated and presents the same 

 general features as the curves obtained with Botrytis spores. 



It is not difficult to find an explanation of the pecuhar shape of the 

 sigmoid curve. We do not know what is the nature of the reaction 

 occurring between the phenol and the spores, whether, for example, it 

 is a chemical combination of the phenol with the protoplasm of the 

 spore, or a physical partition of the phenol between the two solvents 

 protoplasm and water, resulting in the coagulation and death of the 

 spore (cf. Cooper (8, 9)). We are equally ignorant of the nature of the 

 resistance offered by the spores to the poison. It is, however, reasonable 

 to assume that in a large number of organisms, such as those in the 

 suspensions of Botrytis spores, the individuals will differ from one 

 another in resistance, and that if we graduate the resistances and de- 

 termine the number of individuals in each grade (construct, in fact, a 



