Mechanism of immunity against micro-organistm 183 



of Moellcr and their allies, are stained a bright red by neutral red 

 as soon as they are ingested by the phagocytes. It is, therefore, 

 more probable that, in the case of true tubercle bacilli, the reaction 

 in the cells is no longer acid, but alkaline. This conclusion is con- 

 firmed by what is observed in the giant cells of the Algerian gerbil 

 (Mcriones shaii'ii), a species of rodent which exhibits a great natural 

 resistance against the bacillus of human tuberculosis 1 . The bacilli, 

 ingested by these phagocytes, secrete a series of concentric membranes 

 which become impregnated with phosphate of lime (Fig. 5). The 

 process causes the death of the bacilli, of which there remain only 

 the calcified membranes. The precipitation of the lime salt around 

 bacillary membranes itself indicates the alkaline reaction of the 

 medium. The use of certain staining substances fully confirms this 

 conclusion. Thus, with alizarin sulpho-acid the giant cells stain deep 

 violet, this affords clear proof of a very distinct alkaline reaction. 



We arrive then at the general conclusion that phagocytic digestion 

 usually takes place in a medium weakly acid, but that it can also go 

 on in an alkaline medium. It is impossible, in the present state of 

 our knowledge, to define the nature of the acid secreted by the 

 phagocytes. H. Kossel 2 has expressed the view that the intracellular 

 digestion of micro-organisms is effected by the nucleic acid, secreted [194] 

 by the cell nucleus and accumulated in the vacuoles of the contents 

 of the phagocytes. He has brought forward in support of this view 

 the fact that nucleic acid is distinctly bactericidal, killing certain 

 pathogenic micro-organisms, and giving a precipitate composed of 

 albumen and nucleic acid. Later A. Kossel pointed out the presence 

 in these formed elements of albuminoid substances which have 

 an alkaline reaction but which also destroy bacteria. Thus he 

 has isolated from the spermatic fluid of the sturgeon a protamine, 

 "Sturin," which, even in very weak solutions, exhibits a strong 

 bactericidal action on the typhoid bacillus, staphylococcus, etc. It 

 is possible that these substances play a part in intracellular digestion. 

 On the other hand, however, we must regard it as well established 

 that in phagocytes there is a soluble ferment which kills and 

 digests micro-organisms. We have already seen, in connection with 

 the resorption of animal cells, that it is the ferment alexine, or cytase, 

 which plays the principal part in the digestive function. We must 



1 "Lcqons sur la pathologie comparee de 1'Inflamuiatiou," Paris, 1&U2, p. 11*3; 

 authorised English translation, London, 1893, p. 162. 



2 Arch.f. Pkysiol., Leipzig, 1894, S. 200. 



