Facts bearing on acquired immunity 229 



the parasite of recurrent fever. In guinea-pigs, into which blood 

 or serum containing spirilla has been injected on several occasions, 

 the destruction of these micro-organisms is effected in a different [241] 

 way. When Sawtchenko introduced a number of Spirochaete ober- 

 tneyeri into the peritoneal cavity of guinea-pigs so prepared, he 

 noted that they underwent a transformation resembling that ob- 

 served in Pfeiffer's phenomenon. In a short time the majority of 

 these micro-organisms assumed the form of very delicate spirilla to 

 which were attached round granules. There was not a complete 

 transformation of the spirilla into granules, but a portion of their 

 contents exuded in the form of spherical drops. The spirilla that 

 exhibited these changes lost their motility and collected into clumps. 

 There was undoubtedly an extracellular transformation of the spirilla, 

 but this took place only in the peritoneal cavity. When injected into 

 the subcutaneous tissue of a prepared guinea-pig the spirilla brought 

 about the formation of a firm but scanty exudation in this situation. 

 In this exudation were found leucocytes containing spirochaetes which 

 retained their normal form. These micro-organisms were found ex- 

 clusively in macrophages and gave no evidence of the occurrence 

 of Pfeiffer's phenomenon. A like absence of this phenomenon was 

 observed in normal guinea-pigs which had been injected subcutane- 

 ously with the same quantity of spirilla. In these animals, however, 

 the oedema that appeared at the seat of inoculation was abundant 

 and soft, and the disappearance of the spirilla, that is to say their 

 ingestion by the macrophages, took place at a very much later period 

 than in the prepared guinea-pigs. We have, therefore, in this respect 

 a complete analogy with the vibrios : in both cases there is an absence 

 of granular transformation below the skin and an ingestion by the 

 leucocytes of the exudation ; on the other hand, we have Pfeiffer's 

 phenomenon appearing in the peritoneal fluid. This analogy extends 

 even further. Thus, in guinea-pigs prepared by repeated injections 

 of human serum rich in spirilla, Sawtchenko could suppress Pfeiffer's 

 phenomenon in the peritoneal cavity just as easily as in the case of 

 the vibrios. All he had to do was to inject a certain quantity 

 of broth into the peritoneal cavity of his immunised guinea-pigs. 

 Twenty-four hours later, on introducing spirilla into the animals at 

 the same site, they retained their motility for hours, did not exhibit 

 any granular transformation and were ultimately completely ingested 

 by the macrophages. 



These facts lead us to conclude that the fate of the spirochaetes 



