CH. xx.] VACCINATION AND IMMUNITY. 185 



On careful analysis, it will be found that it is not capable of 

 explaining all the facts of the case. As we mentioned in a 

 former chapter, cattle inoculated with blood of a guinea-pig 

 dead of anthrax become affected with anthrax, which, although 

 not fatal, is nevertheless sometimes very severe. The animal 

 recovers, and is now, for a time at least, protected against a 

 second attack. But there is absolutely no ground for the 

 assumption that if an infusion of the tissues of this animal 

 were made, the bacillus anthracis sown in it would not thrive 

 luxuriantly, seeing that bacillus anthracis grows on almost 

 anything that contains a trace of proteids. Similarly when of 

 the tissues of a guinea-pig, or mouse or rabbit, dead of anthrax, 

 an infusion is made, and this is used as nourishing material 

 for bacillus anthracis in artificial cultures, it is found that 

 these latter thrive splendidly. The same fact I have observed 

 in the case of swine-plague. There is then no reason whatever 

 for assuming that, after one attack of illness, the blood and 

 tissues become an unfavourable soil for a second invasion of 

 the same organism, and that this should be due to the exhaus-, 

 tion of some necessary chemical compound. 



There is another theory, commonly spoken of as the Anti- 

 dote Theory (Klebs). According to this, the organisms 

 growing and multiplying in the body during the first attack 

 produce, directly or indirectly, some substance which acts as a 

 sort of poison against a second immigration of the same 

 organism. I am inclined to think that this theory is in 

 harmony with the facts. There is nothing known, from the 

 observations before us, which would negative the possibility 

 of the correctness of this theory ; nay, I would almost say all 

 our knowledge of the life of the micro-organisms points to the 

 conclusion that the different species are associated with 

 different kinds of chemical processes, and that as a result of 

 the activity we find different chemical substances produced. 



The different fermentations connected with the different 

 species of fungi afford striking illustrations of this view. 

 According to this theory, we can well understand that just 

 as in the case of an animal, say a pig, unsusceptible to anthrax 

 the unsusceptibility being due to the presence in the blood 

 and tissues of a particular chemical substance inimical to the 

 growth of the bacillus anthracis so also in the case of a sheep 

 or ox that has once passed through anthrax there is now 

 present in the blood and tissues a chemical substance inimical 

 to the growth and multiplication of the bacillus anthracis 

 whereby these animals become possessed of immunity against 

 a second attack of anthrax. 



