THE CHEMICAL MECHANISMS OF DEFENCE 1161 



up by the same leucocytes when the bacteria have been treated with 

 the serum of an average individual. 



We thus see that immunity, whether innate or acquired, is 

 extremely complex in character and may depend on one or more of 

 many factors. The immunity of an animal to any given infection 

 may be determined by the absence of haptophore groups in his body 

 for the toxin excreted by the microbe responsible for the infection, 

 or by the fact that the haptophore groups are present but are con- 

 fined to tissues on which the toxophore group can have no influence. 

 Thus, e.g., an attachment of the tetanus toxin to a connective- tissue 

 cell would be without effect on the health of the body. Again, 

 immunity may be due to the efficacy of the phagocytes, either of the 

 fluids or the connective tissues, in ingesting and destroying the micro- 

 organism, and this, as we have seen, may again be dependent on the 

 presence or absence in the body-fluids of substances which, while not 

 destroying the micro-organisms, render them more accessible to the 

 action of the phagocytes. In those cases where the infecting organism 

 secretes a specific toxin, the main line of defence and the main factor 

 in the production of immunity is the formation of specific antitoxins 

 to the poison in question. Finally there may be produced as a result 

 of the excess of micro-organisms substances such as the amboceptors, 

 which render the micro-organisms susceptible to destruction by the 

 complements or cytases normally present in the circulating fluids and 

 possibly themselves derived from the activity or destruction of the 

 leucocytes and other phagocytes of the body. 



In this short description we have only been able to touch upon the 

 most salient features of the immunity problem. The question enters 

 strictly into physiology since, as we have seen, it involves adaptations 

 on' the part of the organism to changes in itself or its environment. 

 For the practical application of these facts, as well as the consideration 

 of the minuter details and exceptions, we must refer the student to 

 works especially dealing with the subjects of infectious diseases and 

 immunity. 



