20a MICROBES AND TOXINS s^ 



the vibrio Metchnikowii, a cholera vibrio, becomes much more 

 powerfully bactericidal than the serum of fresh guinea-pigs. "^ 



It is easy to immunize guinea-pigs against lethal doses of 

 the cholera vibrio injected intraperitoneally. Pfeiffer took a 

 guinea-pig thus prepared, injected into it a certain quantity of 

 vibrios, and then abstracted from its peritoneum a little of the 

 exudate. He found that after a few minutes the vibrios had 

 almost entirely disappeared from the peritoneum ; they had 

 been transformed into granules, the first stage of destruction, 

 the " commas " turning into " dots." Later these granules 

 dissolved in the peritoneal fluid like a piece of sugar in 

 water. The same phenomena were observed when the vibrios 

 were injected along with immune guinea-pig serum into the 

 peritoneum of a fresh guinea-pig. 



Pfeiffer's interpretation was that in the immunized body the 

 bacteria are destroyed directly by the body-fluids without the 

 intervention of the leucocytes. 



Such then is Pfeiffer's phenomenon, so long discussed and 

 for long a sort of touchstone in the two immunity doctrines. 

 Metchnikofif and his pupils have subjected it to merciless 

 criticism. First of all they showed that the granule formation 

 takes place also outside the body when the vibrios are mixed 

 with a little fresh serum from an immunised guinea-pig, or even 

 when to the same serum, which from age or heating has lost 

 its complement, a little fresh peritoneal fluid is added. (It 

 was, in fact, while repeating Pfeiffer's experiment that Bordet 

 discovered the two substances in the serum of immune guinea- 

 pigs). In the test-tube, as in the peritoneum, the vibrios fall 

 victim to the action of the complement through the inter- 

 mediation of the immune-body. 



Since the granule formation is due to the combined action 

 of the two substances, and since we know that the leucocytes 

 do not readily shed their complement, which is therefore 



1 It must be said in this connection that the experiment was insufficient 

 to permit a general conclusion on the nature of acquired immunity ; a 

 similar experiment with other bacteria gives a different result and even the 

 vibrio itself when injected mto an immunised animal remains alive in its 

 body for several days. 



