84 PA THOGENIC BA CTERIA . 



A new principle discovered by Pfeiffer, and bearing 

 directly upon the theories of immunity, is that the se- 

 rum of animals immunized to certain diseases (cholera 

 and typhoid) contains a germicidal substance. Metchni- 

 koff has tried to show that the action of this body depends 

 upon solution of the leucocytes, but Pfeiffer has disproved 

 this by showing that the liquor puris from abscesses oc- 

 curring in the experiment-animals did not contain the 

 active substance. 1 



The work of van de Velde 2 is very interesting. An 

 animal immunized by progressively increasing doses of 

 strong filtered toxin produced a serum possessed of pow- 

 erful anti-infectious and antitoxic powers; one immu- 

 nized by the introduction into its body of the washed, 

 precipitated bodies of diphtheria bacilli collected by fil- 

 tration furnished a serum of appreciable anti-infectious, 

 but no antitoxic properties; one immunized by the use 

 of bacillus cultures developed antitoxic and anti-infectious 

 serum identical with the first described; one immunized 

 to weak toxin furnished serum of considerable anti-infec- 

 tious, but slight antitoxic power, and still another ani- 

 mal that received toxin that had been heated developed 

 neither anti-infectious nor antitoxic serum. 



Seeing that the serums commercially manufactured are 

 made by the use of strong filtered toxin, van de Velde 

 examined a number of samples purchased in the market, 

 and found that they were all possessed of both antitoxic 

 and anti-infectious properties. It is important to remem- 

 ber the presence of both of these properties in the serum, 

 as the successful use of the agent for immunizing depends 

 upon the presence of the one, and the use in treatment 

 upon the presence of the other. 



Immunity and antitoxins stand in unknown relation- 

 ship to one another. That an animal has considerable 

 antitoxin in its blood is no guarantee that it is immune. 

 I have seen a horse in each c.cm. of whose blood there 



1 Centra ffil.f. Rakt. it. ranisitsnk., lid. xix., Nos. 14 and 15. 

 * //'it/., Nov. 24, 1897, Bd. xxii., Nos. 18 and 19. 



