BACTERICIDAL OR ANTI-BACTERIAL IMMUNITY. 187 



ever, not been found under the experimental conditions thus far ob- 

 served. ' 



Still it is well known that cells and tissues worn out from use, or 

 dead as the result of injury, inflammatory exudates, etc., are constantly 

 removed from the living body by processes apparently analogous, if not 

 identical with those which can be experimentally evoked. So that auto- 

 lysis in some form seems to be an important factor in the maintenance 

 of the integrity of the body. 2 Just what the agencies are under which 

 normal living tissue cells are protected from the action of autocytolytic 

 substances is not yet clear. But the multiplicity of known "antibodies " 

 justifies the conjecture that such substances anticytolytic may be con- 

 stantly formed and act as safeguards to living and useful cells. 



The Application of Ehrlich's Hypothesis to Cytolysis. If now we turn to 

 the various hypotheses which have been advanced to account for the formation and 

 action of these cytolytic substances, we find that an elaboration of Ehrlich's views as 

 applied to antitoxin is here a source of great illumination. It is evident at once, how 

 ever, that the matter is not so simple as in the case of antitoxin, because we have here 

 two substances at work, the immune body and the alexin. Neither the immune body 

 nor the alexin alone induces cytolysis. They must act together. 



The phenomena are, in the main, accounted for if we assume that it is the alexin 

 which, when the necessary conditions are fulfilled, exerts the destructive action upon the 

 bacterial or animal cell. But the alexin cannot enter under ordinary conditions into 

 direct chemical combination with the cell receptors. The union is effected only by the 

 intervention of the substance which is increased in amount in the process of adaptation ; 

 namely, the immune body. 



A long series of experiments has led to the belief that the immune body has two 

 free atom complexes which enable it to form chemical unions Through one of these 

 atom complexes it unites with the cell to be destroyed , through the other it is joined 

 to the alexin. Then, and not until then, is the alexin so linked to the cell that its toxic 

 or destructive action upon the cell occurs. 



This conception may be illustrated, as in the case of antitoxin, by crude figures. 



Here it should be remembered we are illustrating not the production of the cytoly 

 tic substances, which we shall speak of later, but the action of them upon the cells to 

 be destroyed. 



Let a Fig. 90, A be the cell which is to be destroyed with one of its receptors in- 

 dicated at d. Let b represent the immune body with one atom complex e capable of 

 uniting with the cell receptor d, and with another (/) capable of uniting with the alexin 

 c through g. Now the alexin which appears to be the effective agent in the destruction 

 cannot unite directly with the cell receptor. When, however, it becomes linked to the 

 cell by means of the immune body, b, its destructive capacity can come into play. 



In a similar way one may indicate the action of anticytolytic substances which may 

 be effective through union either with the alexin or with the immune body, as shown 

 in Fig 90, B and C. In B the "antibody " h prevents the linking of the alexin c to the 

 immune body b by itself uniting with the former. It then acts as an. autialexin. In 

 C the "antibody " i prevents the linking of the immune body b to the cell receptor d, 

 and hence acts as an anti immune body. We shall see in a moment why at present the 

 substance here spoken of as antialexiu is usually called the anticomplement. 



The experimental evidence that the auticytolytic substances may be thus due to 



1 Some observations are recorded in which, after profuse internal hemorrhage, 

 haematuria has developed, indicating the possibility of autohaemolysis under special 

 conditions. 



2 See reference to autolj-sis. foot note, p. 92. 



