334 INFECTION AND IMMUNITY. 



duce diphtheria toxin more abundantly. We may 

 assume that the antitoxin combined with the cor- 

 responding receptors situated in the bacilli (diph- 

 theria toxin), and that the bacilli were, as a result, 

 stimulated to produce a greater number of such 

 receptors (toxin). 



Consistent as these observations are with the 

 hypothesis under discussion, Welch meant a great 

 deal more than the immunization of the bacteria 

 against the defensive powers of the animal body. 

 Not only may a bacterium during infection become 

 more resistant to the bactericidal action of the 

 body by producing antibodies for those bactericidal 

 agencies, or by its ability to absorb and dispose of 

 a greater quantity of bacteriolysin ; and not only 

 may a bacterium be able to respond to the presence 

 of natural antitoxins in the body by the produc- 

 tion of more toxin; but, in addition, certain con- 

 stituents of our body fluids may, by combining 

 with suitable bacterial receptors, stimulate the 

 bacterium to the production of a whole shower of 

 cytotoxins, which attack the leukocytes, erythro- 

 cytes, nerve cells, liver, kidney, etc. The nature 

 of the animal substances which may combine with 

 the bacterial receptors and thus cause the forma- 

 tion of the bacteriogenic cytotoxins is left an open 

 question, and is not of essential importance for 

 the theory; it is not at all necessary that they be 

 toxic for the bacterium, and they may even be 

 taken up as food substances. Likewise the possible 

 nature of the cytotoxins produced by the bacterium 

 is of secondary importance. It so happened that 

 Welch assumed that they might be of the nature 

 of amboceptors, which may become complemented 



