854 IMMUNOLOGY 



ing the acute rise of the infection and is greatly enhanced at the time of 

 the crisis, when immunity, which is probably associated with the elabora- 

 tion of antibodies, is developed. Thereafter the infection progressively 

 subsides, unless the immunity is lowered. If the immunity is lowered, 

 the parasites, because their reproduction has not been inhibited, reac- 

 cumulate in the blood until immunity again develops and becomes 

 operative. 



LEISHMANIASIS 



The course of kala azar cannot be studied and analyzed as was done 

 in the case of malaria because its causative agent, Lehhmania donovani, 

 is not accessible for study; but it is of interest here because L. donovani 

 lives in the macrophages themselves, as has been shown by Christophers 

 (1904), Meleney (1925), Hu and Cash (1927), and others. It not 

 only lives in the macrophages of the spleen, liver, bone marrow, and 

 intestinal wall, and, in extreme cases, the macrophages of almost all 

 organs and tissues, but proliferation of the macrophages constitutes the 

 chief characteristic of the disease. For a review of the literature, see C. J. 

 Watson, 1928; Linton, 1929. See the former reference also for a seem- 

 ingly similar condition in the little-known histoplasmosis. The parasites, 

 therefore, instead of being digested, find the cytoplasm of the phagocytes 

 a suitable medium in which to grow and multiply. Splenectomy should 

 be particularly illuminating in trying to decide whether the macrophage 

 system is valuable, imperfect as it is, as the only defense the body has; 

 or is deleterious, as being the most suitable location for the parasites. 

 Some work on kala azar has been done (see Laveran, 1917), but further 

 systematic experimental work on animals should prove valuable. The 

 fact that the disease is so often fatal indicates that reproduction of the 

 parasites is continuous, as in malaria. Immunity, nevertheless, is devel- 

 oped in approximately 10 percent of the infections, but it is not 

 apparent whether the suppression of the infection is predominantly due 

 to an increase in the ability of the macrophages to digest the parasites or 

 to an inhibition of reproduction of the parasites. 



Oriental sore, a cutaneous leishmaniasis caused by L. tropica, on the 

 other hand, usually spontaneously heals and confers an immunity to 

 reinfection. Sections of the skin at the site of the sores often show pro- 

 nounced local accumulations of macrophages. As in the case of the small 



