MECHANISM OF PROTEIN HYDROLYSIS AND IMMUNIZATION 75 



mutual combinations. Two groups of atoms' each of which can 

 unite with a third group may very well unite with each other. 

 But when the antigen has thus combined with an antibody, it 

 no longer has free valences, and so it cannot combine with the 

 cell that it formerly would have entered. In the event that the 

 particular antigen in question was the kind of plotoplasmic prod- 

 uct that we call a toxin, we may well enough call the antibody 

 an antitoxin ; and we may speak of the union of the two as 

 neutralizing the poison and rendering it harmless. But this, of 

 course, applies only to exceptional instances in which the antigen 

 had properties that made its presence objectionable in the cell 

 with which it has affinity. Most antigens that would ordinarily 

 be found in the body have not such harmful properties, and their 

 antibodies, although acting in the same way, would not serve 

 the same purpose. 



But at the moment, of course, I have specifically in mind the 

 antigens that are toxic ; and their specific antibodies are the anti- 

 toxins. And the purport of the present phase of the discus- 

 sion is, it will be recalled, to make it seem plausible, on various 

 analogical grounds, that each and every living cell of the body 

 must on occasion take to itself what we may call antigens, and 

 give out what we may call antibodies ; and that the particular 

 tissues that can produce antibodies in response to any given 

 toxins are precisely those tissues that are receptive to the inva- 

 sion of that toxin. 



If the toxin be one for which the brain tissues have pre- 

 eminent affinity, the antitoxin produced will come from the brain 

 cells. If the toxin be one attacking the liver, the liver cells 

 will furnish the antitoxin. 



However specialized any cell may be to perform pre-eminently 

 a particular function through division of labor in the entire body 

 every cell must retain the primitive capacity to take in nourish- 

 ment and give out excrementitious products, else it obviously 

 could not maintain existence. And it is conceived that the pro- 

 duction of an antitoxin in response to a toxin that the cell can 

 absorb is merely a special manifestation of this primal and funda- 

 mental function. 



The bacterial toxins are, according to the present hypothesis, 

 relatively simple nitrogen compounds of a type suitable for com- 

 bination with various of the body cells not distantly related to 

 the amino-acids ; the production of complementary bodies or anti- 

 toxins by these body cells, under these conditions, may be said 

 to be a commonplace of physiological activity though sharing, 

 of course, in the inscrutability that attaches to all chemical 

 processes. 



