186 PHAGOCYTOSIS 



in the body fluids are derived primarily from the cells which he has 

 classed as phagocytes. According to Schneider, 1 lymphocytes and 

 macrophages seem to contain little or no endolysin, and these cells are 

 not so active in the phagocytosis of virulent bacteria as are the micro- 

 phages. 



It is possible, however, that in certain instances cells not only fail 

 to kill the microparasites they ingest, but actually protect them from 

 circulating antibodies; apparently the microorganisms of leprosy, 

 tuberculosis, gonorrhea, and leishmaniosis may live more or less habit- 

 ually within tissue cells, and, as demonstrated by Roux and Jones, 2 

 living phagocytes are able to protect ingested bacteria from the destruc- 

 tive substances in the surrounding fluid, and even from a potent homol- 

 ogous antiserum. 



Indigestible substances, if chemically inert, may remain in cells, 

 particularly in fixed tissue-cells, for variable periods of time. The leu- 

 kocytes seem to transfer such particles to other tissues, particularly to 

 the lymph-glands. It is probable that these phagocytes are in turn 

 engulfed by the endothelial cells. Macrophages of the lymph-sinuses or 

 the leukocytes may be destroyed in the glands, and their contents re- 

 phagocyted by these cells. In just what manner these insoluble par- 

 ticles reach the gland stroma or perilymphangeal tissues is unknown; 

 it is probable that they are liberated from the lining endothelial cells, 

 and are again seized by the young connective-tissue cells. 



THE RELATION OF THE BODY-FLUIDS TO PHAGOCYTOSIS 

 Important and far-reaching as were Metchnikoff's researches and 

 conclusions, they were not allowed to pass unchallenged, especially by 

 the adherents of the humoral school, who were able to show the potent 

 influences of the body-fluids in the mechanism of recovery from in- 

 fections where phagocytosis was little in evidence, or, indeed, where 

 phagocytosis was impossible. It was shown that Metchnikoff's original 

 theory was untenable, and that the leukocyte is almost impotent if re- 

 moved from the influence of the body-fluids. 



As demonstrated by Denys, Leclef, Fliigge, Nuttall, Pfeiffer, and 

 others, bacteria may be killed, i. e., may undergo a process of lysis or 

 disintegration, by means of substances in the blood-serum entirely in- 

 dependent of phagocytosis Later researches by Wright, Neufeld, and 

 their coworkers demonstrated most clearly that even in those infections 



1 Arch. f. Hyg., 1909, 70, 40. 2 Jour. Exper. Med., 1916, 23, 601. 



