AUTO-CATALYSIS AND INFECTION 113 



A good example of auto-catalysis is quoted by Ostwald in 

 the case of the action of nitric acid in dissolving metals. As 

 has been noticed by several observers, pure nitric acid free 

 from nitrous acid scarcely at first attacks many metals, such as 

 copper, mercury, and zinc, although the impure acid readily 

 oxidises them with production of nitrous acid. If a trace of a 

 nitrite be added, however, the reaction at once commences and 

 momentarily becomes more energetic, as it is continually auto- 

 catalysed with increasing energy by the nitrous acid formed in 

 the reaction. 



The writer has pointed out that such a process of auto-catalysis, 

 induced by a trace of enzyme, may be the means of infection, 

 and of the reproduction of the virus in many of those infectious 

 diseases, such as the acute exanthemata, in which notwithstanding 

 much bacteriological research no causal connection of any living 

 organism has yet been demonstrated. 



The incubation period would be that required for the pro- 

 duction of the auto-catalyst in sufficient quantity to cause a 

 general reaction with the tissue cells. The auto -catalyst, which 

 would act as the toxin of the disease, would still go on increasing 

 in quantity until it had attained the concentration for maximum 

 effect ; but at the same time the tissue cells would react to it 

 as to an ordinary toxin and produce the antitoxin, by which the 

 toxin would be neutralised and rendered inert, and so the course 

 of the disease would be limited. 



The length of time and the exactness of duration of the incuba- 

 tion period form no objection to such a view, for the time of the 

 initial period of auto-catalytic reactions is often prolonged, and 

 the duration of the incubation period would be determined by 

 the reaction of the tissue cells affected, and would but little depend 

 upon the amount of the trace of auto -catalyst which originally 

 carried the infection, unless this were very large. 



Further, it may be pointed out that in many cases in which 

 the toxin arises from the products of bacterial growth, the length 

 of the incubation period depends upon the period of reaction of 

 the tissue cells, and not upon any cycle of development of the 

 parasite, as, for example, in enteric fever, where the Bacillus 

 typhosus possesses no period of growth corresponding to the period 

 of incubation. 



Finally, variations in immunity in different individuals here, 



