IMMUNITY, IMMUNIZATION, AND CURE. 61 



istence of immunity is not to be explained upon the basis 

 of this bactericidal activity, as there is a want of the neces- 

 sary relation between the degree of bactericidal activity and 

 that of natural immunity. White rats, to the bactericidal 

 activity of whose blood reference has already been made, 

 are not absolutely immune to anthrax, and the blood-serum 

 of dogs, which possess a considerable degree of immunity 

 to this disease, constitutes an admirable culture-medium for 

 anthrax-bacilli. It is, further, questionable whether the 

 alexins exhibit the same activity in the organism as in the 

 test-tube. According to Buchner's view this is the case. 

 Only in the capillaries, where the bacteria accumulate and 

 are thus washed by but little blood, is the influence of the 

 alexins not equally manifest. 



What has been said of congenital immunity is applicable 

 also to acquired immunity. Only in exceptional instances 

 is there a proper relation between the bactericidal activity 

 of the blood-serum and artificial immunity as, for instance, 

 after vaccination of guinea-pigs against the vibrio of 

 Metschnikoff, when the blood acquires bactericidal activity. 



The bactericidal activity of the remaining bodily fluids is, 

 in general, less than that of the blood-serum. Such activity 

 has been observed in the aqueous humor of the eye, in all 

 possible exudates and transudates, and even in the saliva 

 and nasal mucus. The bactericidal activity of all these 

 fluids is, however, neither constant nor proportionate to the 

 degree of immunity present. 



The alexins appear to arise from the leukocytes, and to 

 represent their secretory products. Denys and his pupils 

 demonstrated experimentally that the bactericidal activity 

 of the serum increases or diminishes with the larger or 

 smaller number of leukocytes respectively. Buchner and 

 Hahn obtained analogous results, and the view of the 

 Munich school may be expressed as follows : the leuko- 

 cytes constitute an important factor among the natural pro- 

 tective forces of the organism through substances in solution 

 secreted by them. Metschnikoff also assumes as established 

 the fact that a certain relation exists between the bactericidal 

 activity of the blood and the number of leukocytes ; and 

 he adds that with the death of the phagocytes, which takes 

 place abundantly on abstraction of blood, a portion of these 

 bactericidal substances is set free, and it is these that repre- 

 sent a large portion of the alexins of the serum. 



