230 MECHANISM OF INFECTION AND IMMUNITY 



processes. The body cells have begun the contest against the invaders. 

 Since the invasion began they have been preparing for the war and 

 now the battle has begun. The bacilli have gained entrance and multi- 

 plied at the expense of the soluble proteins of the body because the 

 animal cells were not at first prepared to combat them. Now they have 

 developed bactericidal and bacteriolytic ferments and opsonins, possibly 

 antitoxins, and with these the further development of the bacteria is 

 to be contested. When the infecting organism is a toxin producer, like 

 the diphtheria or tetanus bacillus, it is not the cellular substance of 

 the bacteria which directly and immediately endangers the body cells, 

 so much as its soluble product, the toxin. In this case, the contest is 

 decided by the ability of the body cells to elaborate and make available 

 enough antitoxin to neutralize the bacterial toxin. In this case, the 

 therapeutic administration of antitoxin has secured to curative medi- 

 cine its greatest triumph, and success or failure depends on the early 

 administration of this magical cure in sufficient amount. The cells 

 of the horse have been trained to produce this body and now it is 

 poured into the blood current of the child to save its cells from destruc- 

 tion. The diphtheria bacilli contain a cellular poison, quite different 

 from the toxin, but since the bacilli, except in small numbers, are not 

 in the child's blood and tissue, but in its throat, the cellular poison 

 may be neglected, for as a rule the few in the body do not contain 

 enough poison to endanger the life of the child. Cure, then, depends 

 on the neutralization of the toxin before it has done irreparable harm. 

 When the infecting bacterium is one best combated by phagocytes, 

 the body cells supply opsonins which, in some way yet unknown, ren- 

 der the invaders less resistant to the leukocytes. In these cases, the 

 result depends on the effectiveness with which both the fixed and 

 mobile cells of the body perform their functions. One of the important 

 factors is the number as well as the virulence of the invading bacteria 

 at the time when the contest begins. The greater the number, the more 

 must the phagocytes devour, and feeding is a limited function. The 

 more virulent they are, the less effective will be the opsonins. Rosenow 

 has shown that the opsonins are not effective against the more virulent 

 strains of streptococci and that infection with these generally proves 

 fatal. It is worthy of note that bacteria devoured by phagocytes do 

 not endanger the life of their host to the extent and in the same way 



