186 BACTERICIDAL OR ANTI -BACTERIAL IMMUNITY. 



these various cytolytic sera aud their mode of action is analogous with 

 those in hsemolytic sera. Here, as there, the action is due to two groups 

 of substances: one, the "immune body," stable and increased by the 

 adaptive process ; the other, the alexin, occurring normally in the body, 

 not increased in adaptation, and readily destroyed or rendered inactive 

 by heat. 



All of these last-mentioned forms of cytolytic sera require more ex- 

 tended study before far-reaching conclusions should be drawn from them. 

 But it is now evident that the different functional types of cells in one 

 animal are capable in the adaptation to the economy of another of incit- 

 ing more or less definitely specific responses, as shown by the various 

 types of cytolytic sera which are formed. 



When one musters all the possible combinations in this form of adap- 

 tation and considers the probability that multiple immune bodies may 

 develop in each instance, and that these furthermore may correspond to 

 multiple alexins, the complexity of artificial cytolysis becomes evident. 



But now still another phase of this subject demands a word. These 

 cytolytic or, as some prefer to call them, cytotoxic sera, when introduced 

 into the living bodies of the species from which the cells inciting their 

 formation are derived, act as toxins to which the organism responds, 

 each after its kind, by the development of antitoxic substances. These 

 are called anticytolysins or anticytotoxins. 



Let us look at an illustration of this interesting point. The blood 

 serum of the normal guinea-pig has, as we have seen, no lytic action on 

 the red blood cells of the rabbit, but after the adaptation of the guinea- 

 pig to the blood of the rabbit by repeated iutraperitoneal injections, the 

 guinea-pig serum is strongly lytic for the rabbit corpuscles in test tubes 

 outside the body. But this lytic serum is not less toxic when introduced 

 into the body of the rabbit. Under these conditions the rabbit produces 

 an antitoxin, an antihsemolytic substance, which is in solution in his 

 serum. If a little of this antihsemolytic serum be mixed with some of 

 the lytic serum from the adapted guinea-pig, it will be found, on the 

 addition of rabbit corpuscles, that the lytic serum has lost its power, just 

 as diphtheria toxin loses its harmful properties on mixture with diph- 

 theria antitoxin. Thus may be formed a great variety of specific "anti- 

 bodies" anticytolysius from sera which are normally lytic or have 

 become so through experimental adaptations. 



In view of the remarkable results of the adaptation of the body to 

 alien cells from different animal species which we have reviewed, it was 

 natural to ask how an animal would respond to the introduction into the 

 recesses of his body of cells red blood corpuscles, for example from 

 another individual of the same species. It was found, in fact, that 

 under these circumstances lytic substances are sometimes, though not 

 uniformly, developed. The possibility of the formation of isolytic sub- 

 stances was thus established. But if this be possible, why, it was asked, 

 may not autolytic substances be formed by the adaptation of an animal 

 to his own cells experimentally displaced? Such substances have, how- 



