90 ANTIGENS AND ANTIBODIES 



demonstrated by injecting a normal animal with a minimal fatal 

 dose of the corresponding bacteria together with an appropriate 

 quantity of serum obtained from an "immunized" animal. In 

 such an event death does not result, because the animal has here 

 been passively immunized by the serum of the immune animal, 

 and now in turn develops an active immunity as the result of the 

 introduction of the bacteria. 



In a previous chapter we have seen that the bacteriolytic action 

 of normal serum is referable to the associated activity of two sub- 

 stances, viz., the thermolabile complement and the thermostabile 

 amboceptor. On studying a bacteriolytic immune serum in this 

 direction, it may be shown that here also the destructive action upon 

 the bacteria is dependent upon complement and corresponding 

 amboceptor, and that its greater degree of activity as compared 

 with normal serum is altogether owing to an increased content of 

 the latter. 



At a time when the antibacterial action of the normal blood serum 

 was first discovered the question of the origin of the "alexins" was 

 wrapped in complete obscurity. In view of the manner in which 

 the production of the immune amboceptors takes place there can 

 be no doubt that a direct connection exists between their appear- 

 ance and the introduction of the corresponding bacteria, and upon 

 injecting different animals with different species of bacteria we obtain 

 evidence of a most remarkable specificity in the nature of the response, 

 which one can well compare to the vibratory response which is called 

 forth in tuning forks of different pitch by striking forks of corre- 

 sponding pitch. 



Further studies in this direction have shown that the appearance 

 of such immune amboceptors takes place according to a fairly 

 definite rule : immediately following the injection a period of latency 

 can thus be observed which lasts for a few days and is then followed 

 by a critical ascent of the curve leading to a maximal point from 

 which there is in turn a corresponding drop which at first is fairly 

 abrupt and later more gradual, and hence a slow return to previously 

 existing conditions. As the same result is obtained after the injec- 

 tion of dead bacteria it is clear that the prolonged effect which 

 follows the introduction of the organisms cannot be referable to pos- 

 sible variations in their number which one might otherwise imagine 

 to be operative on different days and at different hours, nor can the 



