182 



Chapter VII 



micro-organisms and of the intracellular granules takes place. When 

 neutral red is added to an exudation in which the leucocytes are 

 dead, the staining of the ingested micro-organismsdead or living- 

 does not take place. I have myself verified 

 these observations, and Himmel 1 , who has 

 carried out an elaborate investigation on 

 this subject in my laboratory, has con- 

 firmed them in numerous cases. In the 

 third and fourth chapters of this work I 

 have already brought forward arguments 

 in favour of the view that the staining of 

 the ingested elements indicates a feebly 

 acid reaction inside the phagocytes. Some- 

 times this reaction manifests itself in the 

 digestive vacuoles ; in other cases it is ex- 

 hibited only in the micro-organisms directly 

 lodged in the protoplasm (Fig. 38). Whilst 

 the phagocyte is still living the acid juice 

 which fills the vacuoles or permeates the 

 ingested organisms does not mix with the 

 protoplasm which is always alkaline. But 

 shortly after the death of the phagocytes 

 this mixture is effected without difficulty, 

 and the alkalinity of the protoplasm is then 

 amply sufficient to neutralise or even render 

 alkaline the feebly acid juices. This in- 

 terpretation of the facts is in complete 



harmony with all the data, collected up to the present, on the staining 

 by neutral red of phagocytised micro-organisms. 



All ingested bacteria do not, however, stain in the way we have 

 indicated. Tubercle bacilli, even in cases of natural immunity, 

 remain unstained inside the phagocytes or take on only a very slight 

 straw-yellow tint. Himmel made this observation on the bacilli of 

 avian tuberculosis that had been ingested by the peritoneal leuco- 

 cytes of the guinea-pig, a species resistant to this micro-organism. 

 It might be thought that such a resistant membrane as that of the 

 tubercle bacillus, with its waxy layer, would prevent the penetration 

 of the acid leucocytic juice; but several bacilli which resist de- 

 coloration by acids, as do the tubercle bacilli, notably the bacilli 

 1 Ann. de VInst. Pasteur, Paris, 1901, t. xv, p. 928. 



Fio. 38. Peritoneal macro- 

 phage of guinea-pig that 

 has ingested a number 

 [193] of Bacilli coli. Stained 

 infra vitam with neutral 

 red. 



