38 QUATERCENTENARY STUDIES IN PATHOLOGY 



When anti-plague serum has been injected into the animal 24 hours 

 before the bacillus, there is observed, during the first hour, an increase in 

 mononuclear leucocytes, around which the bacilli are clumped, some 

 of them being englobed by the mononuclear leucocytes. After the first 

 hour the polynuclear leucocytes multiply rapidly and englobe the bacilli, 

 so that in three hours no free bacilli, and in six hours no bacilli 

 either intra or extra-cellular, are observable. The exudate now consists 

 entirely of polynuclear leucocytes. The animal in this case recovers. 



When the number of bacilli is so great that the resistance conferred 

 by the serum is insufficient to protect the animal, the bacilli which 

 remain undevoured by the phagocytes continue to multiply till the death 

 of the animal results. 



The bacilli lying free and those within the mononuclear leucocytes 

 retain their normal morphology and staining reactions, whereas, those 

 within the polynuclear leucocytes tend to stain badly and to assume 

 coccal-like forms. 



In regard to the nature of the action of the serum in relation to 

 phagocytosis, Markl says : — " To determine whether the injection of the 

 immune serum has an influence on the cells of the body, or whether the 

 bacilli are directly influenced, the following experiment was performed. 

 A suspension of plague bacilli in normal salt solution was added to 

 inactivated immune serum, and the mixture was placed three hours in 

 the incubator. After centrifugalisation the clear fluid was pipetted from 

 the sediment, which, after being several times washed with salt solution, 

 was injected intraperitoneally into rats. These bacilli thus acted on by 

 the immune serum behaved in the animal body exactly like bacilli which 

 had been injected along with free immune serum. They were englobed 

 by the phagocytes. 



The phagocytosis occurred so rapidly and was so extensive that no 

 doubt remains that the immune serum has a direct influence on the 

 bacilli, entering into union with them and conferring on them a positive 

 chemiotaxis." * 



He concludes that in the case where bacilli of low virulence are 

 injected extracellular bacteriolysis plays an important part, whereas, 



* A discussion of the relation of Markl's work to the views of Douglas and Wright is 

 avoided in this paper as of too controversial a nature. 



(148) 



