PHAGOCYTOSIS 265 



ihe case of engulfed living cells, it seems probable tbat tliey must be 

 first killed — they form no exception to the rule that living protoplasm 

 t-annot be digested. This brings forward the (juestion of so much 

 importance in the problems of innnunity : Do living bacteria enter 

 phagocytes, or are they first killed by extracellular agencies before 

 they can be taken up ? At the present time it seems to be positively 

 established that leucocytes do take up bacteria which are still viable, 

 and which may either grow inside the leucocyte or may be destroyed 

 by intracellular processes.^" On the other hand, leucocytes do not 

 take up extremel}" viiiilent bacteria, and hence the question as to the 

 relative importance played by the leucocyte and b}' the body fluids is 

 still undetermined. It is probable that phagocytosis by fixed tissue- 

 cells is of much less importance in checking bacterial growth than is 

 phagocytosis by leucocytes. Thus Ruediger's experiments showed 

 that emulsions of organs, with the exception of bone-marrow, do not 

 destroy streptococci which are readily destroyed by leucocytes. How- 

 ever, the phagocytic activity of certain endothelial cells, especially in 

 lymph sinuses and the Kupffer cells of the liver, is so great that these 

 cells may equal or surjDass the leucocytes in bactericidal power. 

 Leucocytes do not seem to bind bacterial toxins.^" 



Indigestible substances may remain in cells, particularly in fixed 

 tissue cells, for very long periods, if the substances are chemically in- 

 ert. The leucocytes seem to transfer the indigestible particles which 

 they have engulfed to other tissues, particularly to the lymph-glands ; 

 this is probably accomplished by phagocytosis of the laden leuco- 

 cytes by the macrophages of the lymph sinuses, but how the insoluble 

 particles are later transferred to the gland stroma or perihT^nphangial 

 tissues, where they are chiefly found in such conditions as anthracosis, 

 etc., is quite unknown. 



Leucocytes contain substances which are strongly' bactericidal, in- 

 dependent of the action of the blood serum, and which have been 

 called cndolysins; *^ they are resistant to 65° or even higher, and seem 

 to be bound rather firmly to the protoplasm of the leucocytes, for they 

 resist extraction except by vigorous methods; they have a complex 

 structure like the amboceptor-complement bacteriolysins of the serum,, 

 and are not specific (Weil).*'* They do not pass through porcelain 

 filters readily, are precipitated by saturation with ammonium sul- 

 phate, and resemble the enzymes in many respejcts.^° It is probable 

 that the endolysins act upon bacteria that have been phagocyted, and 

 perhaps also upon free bacteria when liberated in suppuration through 



46 See Riiediger, Jour. Amer. Med. Assoc, 100.5 (44). 108. 



•*'■ Fetter sson, Zeit. Imnuinitiit.. 1011 (8), 408. Kohzarenko, however, states 

 that horse leucocvtes neutralize diphtheria but not tetanus toxin. (Ann. Inst. 

 Pasteur, 1915 (29). 190.) 



*s For general review see Kling, Zeit. Ininiunitat., 1910 (7), 1. 



49 Arch. f. Hyg., 1011 (74), 289. 



soManwaring, Jour. E.xp. Med., 1912 (16), 250. 



