530 INFECTION AND IMMUNITY. 



teria and the destruction of bacteria by the leuco- 

 cytes which constantly appear on the mucous sur- 

 face are probably important factors in this local 

 resistance. Congestion of these surfaces, espe- 

 cially the tonsils, from any cause, as from ex- 

 posure, or the occurrence of some other infection, 

 as may be the case in scarlet fever, may lower the 

 local protective powers. And, as stated, the serum 

 and plasma which exude in catarrhal conditions 

 or other inflammations, provide a medium which 

 favors the growth and development of virulence 

 by streptococci. 



Concerning the conditions which, in the body, 

 antagonize infection, we are largely in the dark. 

 It has been impossible to demonstrate antitoxic 

 and bactericidal substances in the normal serum 

 of man. Streptococci grow freely in fresh normal 

 serum which contains no leucocytes (Weaver and 

 G. F. Euediger). Phagocytosis of streptococci 

 first came under the observation of Metchnikoff, 

 who in 1887 noted it as a striking occurrence in 

 erysipelas. Only the microphages took up the cocci. 

 The marked leucocytosis which is noted clinically 

 suggests, but of course does not prove, that the 

 leucocytes take an active part in the destruction 

 of the cocci. Experimental work showing such a 

 relationship is not lacking, however. Bordet con- 

 cluded that all the protection which guinea-pigs 

 and rabbits show against streptococci is due to 

 the phagocytes. In actual infection streptococci 

 have often been found within the leucocytes of 

 the blood and inflammatory exudates (G. F. Eue- 

 diger.) Non- virulent or weakly virulent strains 

 are phagocytized more readily than the virulent in 

 experimental work. Euediger also demonstrated 



