IMMUNOLOGY 853 



The fact has been stressed that the greatly enhanced phagocytic activity 

 of individual macrophages during acquired immunity is specific and is 

 probably related to antibodies. In addition, there is a nonspecific increase 

 of macrophages at strategic points, particularly in the spleen and the 

 bone marrow, due to their cytogenesis from lymphocytes through poly- 

 blast stages and from histogenous macrophages. The latter source is 

 acknowledged by Bruetsch (1927, 1932a, 1932b) and others, and both 

 sources have been demonstrated by W. H. Taliaferro and Cannon 

 (1936) and W. H. Taliaferro and Mulligan (1937). In fact, the chief 

 source of new macrophages is from lymphocytes (PI. 3). The lympho- 

 cytes themselves arise by mitotic proliferation (PI. 4). This is a promi- 

 nent part of the so-called lymphoid hyperplasia of the spleen and occa- 

 sionally of other organs, if the malarial infection is long drawn out. 



In passing it may be mentioned briefly that the parasites destroy red 

 blood cells in large quantities, flood the blood plasma with foreign mat- 

 ter such as corpuscular debris, free malarial parasites and malarial pig- 

 ment, sometimes block the capillaries and damage various tissues, espe- 

 cially the spleen and liver. All these losses and destructions are made 

 good by various nonspecific hyperplastic and reparative activities of the 

 host. The pathological and regenerative changes have been extensively 

 studied, especially in human malaria (see W. H. Taliaferro and Mulli- 

 gan, 1937, for a review of the literature) . 



The foregoing results indicate that acquired immunity against malaria 

 largely involves parasiticidal effects, with no pronounced inhibition of 

 the rate of reproduction for extended lengths of time. The parasiticidal 

 effects can be correlated with phagocytosis. Phagocytosis is sluggish dur- 



CAPTION FOR PLATE ON FACING PAGE 



Plate 4. A nodule in the white pulp of the spleen during lymphoid hyperplasia as- 

 sociated with the late acute rise of Plasmodium cynomolgi in a rhesus monkey. (From 

 W. H. Taliaferro and H. W. Mulligan, "Histopathology of Malaria with Special 

 Reference to the Function and Origin of the Macrophages in Defence," Indian Medical 

 Research Memoirs, No. 29 [May, 1937], pp. 1-138.) 



Figure 1. This activated splenic nodule due to malaria is slightly enlarged, shows a 

 pronounced transitional zone and a markedly active secondary nodule, in which occur 

 swollen phagocytic reticular cells and mitoses, among many lymphocytes and a few reticu- 

 lar cells. X 180. 



Figure 2. A detail of the upper portion of the secondary nodule shown in Figure 1 

 which consists mainly of medium lymphocytes and swollen, slightly phagocytic reticular 

 cells. Reticular cell A is beginning to mobilize. X 1015. 



Figure 3. A detail of the lower portion of the secondary nodule shown in Figure 1, 

 which consists mainly of lymphocytes many of which are dividing. X 655. 



