264 
the “ tadpole ” type was found. In the sub-inoculations, however, 
“ stumpy " forms made their appearance. At Lokandu the “tadpole' 
and “ stumpy ” forms were seen. At Kasongo “ long " forms were seen 
on one cow, and "tadpole " forms in the others. In one of these a 
"long’’ form was also observed. The “stumpy and "long"types 
was also seen in the antelope at Kasongo. Dutton and Todd 
described the “ tadpole ” as being present at the beginning of the 
disease, while the other forms of the parasite appeared later. 1 ' 1 
It seems quite probable that the “ tadpole ” forms are really often 
present in chronically infected animals and that they give place to the 
“ stumpy ’’ and “ long " forms, as the disease becomes more acute, in 
either the original host or in sub-inoculated animals. That this is a 
probable explanation is supported by several observations in the 
present paper. For example, the history of the parasite as observed 
in the case of Yolo (p. 253), where we have the change from the minute 
form to the other two types in the sub-inoculations. The similar change 
seen by Broden 3 in the case of his sheep and its sub- inoculation is of 
interest in this connection. Broden states that in the animals sub¬ 
inoculated from the cattle at Yumbi, the trypanosomes preserved the 
characteristics of those seen in the original animals. This observation 
seems to conflict with the explanation we have just given. He does 
not state definitely that forms with a free flagellum were absent, and 
fiom the fact that he compares some of his forms with the hyaline 
ones of Bradford and Plimmer which had a free flagellum, it seems 
possible that one was also present in some of the trypanosomes he saw. 
In this connection it is interesting to note that he observed only the 
petite forms in the cattle at Eala, whereas we saw both the "tad¬ 
pole and the long forms. The occurrence at the same time of 
trypanosomes of more than one of the types in several of our animals 
certainly also seems to point to the infection being caused by only one 
trypanosome rather than by two or more. 
(2) Animal Reactions. The virulence of various strains of 
trypanosomes (in the laboratory) may vary greatly. The effects of a 
parasite on experimental animals can therefore only be taken as a 
general indication and cannot be accorded specific value. A parasite 
can only be said roughly to be highly, fairly, or slightly virulent. 
With Trypanosoma dimorphon the Congo parasites come under the 
second class. 
