CHAPTER VI. 

 THE BACTERICIDAL SUBSTANCES OF THE BLOOD. 



WE have seen in the foregoing chapter that the outcome of a 

 bacterial invasion will of necessity be influenced by the phagocytic 

 defence of the body, but that this in turn is largely dependent upon 

 the presence of certain auxiliary factors in the body fluids. The 

 recognition of the interdependence of these two elements is most 

 important, as it has in a measure served to unite the two opposing 

 factions of immunity students, between which a deadlock had prac- 

 tically developed, viz., the cellular school, headed by Metschnikoff, 

 and the humoral school of Pfeiffer and Ehrlich, who looked upon 

 the phagocytic activity of the leukocytes, and certain bactericidal 

 properties of the body fluids respectively, as the essential protective 

 mechanism of the body against bacterial infection. 



Alexins. That the blood-serum per se really possesses active bac- 

 tericidal properties had been demonstrated already by Fodor, Nuttal, 

 and Buchner. The latter ascribed the bactericidal action of blood- 

 serum to substances which he assumed to be of the nature of ferments, 

 and which he designated as alexins. Subsequent studies, which are 

 intimately associated with the names of Ehrlich and Morgenroth, 

 Bordet, Neisser, and Wechsberg, etc., have then shown that the 

 bactericidal action of the serum is dependent upon the presence of 

 two substances, one of which serves as a connecting link between 

 the bacteria and the second substance, and which has been vari- 

 ously termed intermediary body (Ehrlich and Morgenroth), substance 

 sensibilisatrice (Bordet), fixateur (Metschnikoff), but which is now 

 generally spoken of as amboceptor (Ehrlich), whereas the second 

 substance has been designated as alexin (Buchner and Bordet), 

 cytase (Metschnikoff), or complement (Ehrlich and Morgenroth). 



Of these two substances the complement is thermolabile and 

 destroyed by heating for 30 minutes at 56 C., while the amboceptor 

 is relatively thermostabile, being rendered inactive only at a tempera- 

 ture of 68 to 70 C. The complement itself is incapable of combining 



