166 TROPICAL MEDICINE AND HYGIENE 



vacuoles are seen in it. The parasites can also be stained 

 by many of the basic aniline dyes, weak carbol-fuchsin 

 and carbol-thionine perhaps giving the best results. 



In smears obtained from the liver and spleen during 

 life the parasites may either be free or contained in cells 

 or embedded in a matrix. The matrix is not seen in 

 smears made from organs after death, nor in sections 

 in which the parasites always appear to be intracellular. 

 In the great majority of cases the cells containing the 

 parasites appear to be endothelial cells of capillaries and 

 lymph spaces, either unaltered or of large size and 

 irregular shape, constituting macrophages. The macro- 

 phages often contain large numbers of parasites, upon 

 which they appear to exert no phagocytic action. On 

 the contrary, under the influence of the parasites the 

 macrophages undergo gradual disintegration, and in all 

 probability furnish the matrix seen in ante-mortem smears, 

 and the parasites are alive and capable of developing into 

 flagellate forms. 



Next to the endothelial cells the large mononuclear 

 leucocytes most frequently harbour the parasites, and 

 a few are found in the polymorphonuclear leucocytes; 

 they also occur in the myelocytes of bone-marrow, but 

 are not met with in parenchymatous cells. 



When obtained post mortem, and especially if several 

 hours have elapsed since the death of the patient, many 

 of the parasites show changes indicative of development. 

 They are larger, 3 //, to 5 //, in diameter, the chromatin 

 masses show signs of division and may even be re- 

 duplicated, and commencing cleavage of the cytoplasm 

 is seen, each half containing a large and a small chromatin 

 mass. 



In sections, owing to shrinkage, the parasites appear 

 much smaller than in smears ; the chromatin masses are 

 closer to each other and the smaller has frequently lost 

 its rod-shaped appearance. 



Etiology. The etiology of kala-azar is of special in- 

 terest, both because of the repeated failures which have 



