PASTEUR AND CHAUVEAU 243 



in effect, toxins that is, they are defensive poisons which have 

 been evolved as means of protection against animal enemies, insects 

 or herbivora. Usually such toxins, besides being poisonous, have 

 an unpleasant taste. As is well known, use enables the individual 

 to tolerate immensely increased doses of some vegetable poisons, 

 such as nicotine and opium ; in other words, a high degree of 

 immunity may be acquired. The vegetable toxins abrin, ricin, and 

 crotin are probably of a proteid nature, resembling the toxins of 

 disease in having a very complex chemical composition. In the 

 case of each of them it is possible to manufacture an antitoxin 

 protective against the corresponding toxin, (r) If the yeast fungus 

 be placed in a solution of sugar it consumes the latter and excretes 

 alcohol. Alcohol is not a toxin, a defensive weapon, but a waste 

 product, comparable to the urine of man not to the venom of 

 snakes. When it attains a certain strength (about 14 per cent.) in 

 the solution the fungus perishes just as the cells of a man's body 

 perish if his excreta be retained as in kidney or liver disease. 



407. Here we have a confused mass of data, culled from many 

 sources. Our task is to ascertain the relations of the facts and so 

 link them together, so systematize them, as to discover, if possible, 

 how immunity is acquired. Pasteur supposed that each species of 

 microbe finds in the body of its host a special pabulum, the ex- 

 haustion of which results in the starvation of the microbes, and 

 therefore in immunity permanent if the pabulum be not renewed, 

 temporarily if it be renewed. But Nature has evolved both man 

 and microbes as bundles of adaptations. It would be strange if 

 man possessed a series of pabula which are not necessary to his 

 well-being for he lives very well after recovery but which render 

 him liable to disease. Chauveau supposed that the microbes like 

 yeast, are killed by the concentration of their own excreta, and 

 that immunity is permanent or temporary accordingly as these 

 waste products are permanently bottled up within the body, or 

 eliminated. But waste products are usually less inimical to the 

 organism producing them than to most organisms to which they 

 are strange. Thus yeast fungi are able to live in a solution in 

 which the percentage of alcohol is as high as thirteen or fourteen ; 

 but no man could live if alcohol formed anything like that propor- 

 tion of his total body weight. Both Pasteur's and Chauveau's 

 hypotheses are decisively negatived by the fact that microbes may 

 flourish in sera taken from immune individuals. 



408. Highly popular is, or was, the hypothesis that microbes or 

 their hosts produce substances (the antitoxins) which chemically 



