THE TRYPANOSOMA BRUCII. 468 



ill close apposition to each other. 'LMieu the outlines of the 

 individual organisms become indistinct and they apparently 

 fuse together, so as to form a plasmodium, consisting of a 

 mass of protoplasm containing micro- and macro-nuclei, 

 similar to that seen in the spleen and in blood from the lungs 

 of rats and mice. It is principally on account of this 

 appeai'ance in the blood of spleenless animals that we think 

 it possible that the formation of this plastnodial form is due 

 to fusion of adult forms, and a similar process also occurs in 

 related organisms. The detachment of flagellated amoeboid 

 forms from these masses can be always seen. The amoeboid 

 forms are always present in the bone marrow and glands of 

 spleenless animals. 



None of the animals we have used have been found to be 

 immune against the Trypanosoma Brucii. They have all 

 died at varying periods, from five days — which is the shortest 

 time in our experiments — in the case of the rat, to eighteen 

 weeks — which is the longest period — in the case of the guinea- 

 pig. But there is probably in all animals some attempt at 

 resistance, and this, so far as we have seen, is by phago- 

 cytosis. We have only observed phagocytosis of the amoeboid 

 form of the organism, and never of the adult forms. We 

 have seen this occur in the peritoneal fluid of the guinea-pig, 

 in the spleen of the rat and mouse, and in the blood of the 

 spleenless dog and cat. We have, in figs. 44 and 45, shown 

 phagocytosis occurring in the blood of a spleenless cat, in 

 which animal it can, in our experience, be most easily 

 observed. Tiiis cat died in twelve days, whereas the average 

 time the normal cat lives after inoculation is about twenty- 

 five days. All the animals from which we have removed the 

 spleen previous to inoculation have died in a shorter time 

 than the normal animal, so that probably there is, in the 

 earlier stages of the disease, a good deal of phagocytic actioTi 

 taking place in the spleen. 



