248 RESISTANCE AND IMMUNITY 



venoms of snakes; moreover, Bordet,^ as well as Belfanti and Carbone,^ 

 have established the fact that the serum of an animal into which the 

 defibrinated blood of another species has been repeatedly injected, 

 acquires the power of hemolyzing the red cells of this serum. Quite 

 similarly, the repeated injection of spermatozoa^ may finally lead to 

 the production of a blood-sermn which acts destructively upon 

 these elements. Reactions of varying specificity have also been 

 obtained with ciliated epithelium, mucous tissue, pancreas, and 

 kidney substance. 



In general it may be said that the blood and tissue-fluids are capable 

 of inciting any one of the following reactions : 



(a) A destruction of red corpuscles, hemolysis. 



(6) A destruction of other types of cells, cytolysis. 



(c) A destruction of bacterial cells, bacteriolysis. 



(d) An agglutination or clumping of cells of different kinds, inclu- 

 sive of bacteria. 



(e) A precipitation of the cytoplasm. 



(/) A coagulation of the cellular contents. 



The substances by means of which these reactions are brought 

 about, are designated respectively as hemolysins, cytolysins, bacteri- 

 olysins, agglutinins, precipitins, and coagulins, but only the last four 

 of these play a part in the production of that type of immunity which 

 is specifically directed against pathogenic bacteria. 



Nature of the Reaction. — Two theories are commonly held to 

 explain bacterial immunity. Thus, it has been suggested by Roux, 

 Buchner, and others that the antitoxic substances or antitoxins do 

 not attack the toxins directly, but destroy them in an indirect way 

 by rendering the body more resistant against them. In the second 

 place, it has been proposed by Ehrlich, Behring and others that a 

 specific interaction occurs between the antitoxin and the toxin in the 

 nature of an ordinary chemical reaction. The evidence so far pre- 

 sented by different observers favors the latter view and, hence, it 

 must be concluded that the union between the antitoxin and the toxin 

 is dependent upon the presence of two distinct bodies which inter- 

 act in accordance with the laws of valency. The chemical nature of 

 this process is betrayed by the fact that concentrated solutions are 

 more effective than dilute, and that it is accelerated by heat and re- 

 tarded by cold. 



In accordance with the accepted view pertaining to chemical 

 neutralization, Ehrlich assumed that the molecule of the toxin con- 

 sists of two separate groups or atoms, one of which unites with the 

 antitoxin and binds it, while the other brings its specific action to 

 bear upon the latter. The intermediary or anchoring portion is desig- 



1 Ann's de I'inst. Pasteur, 1896. 



2 Giron. della R. Acad, di Torino, 1898. 



' Metchnikoff, Ann's de I'inst. Pasteur, 1898, or Landsteiner, Centralbl. fiir 

 Bakterienk., i, 1899, 25. 



