Have Trypanosomes an Ultra-microscopical Stage? 395 
developing outside the body into a clearly visible flagellate. It is evidently 
important, then, in studying such diseases as South African horse-sickness, to 
try the effect of planting out the blood on various media, and looking for a 
visible stage of development in different insect hosts. 
The following experiments were made to test the truth of the statement 
that trypanosomes have this invisible stage. The filters used were Berkefeld’s 
ordinary filters for laboratory use. They were tested before use and found 
to readily keep back Micrococcus melitensis from the filtrate. The apparatus 
was attached to a Sprengel’s pump :— 
To ascertain if the Filtered Blood of Rabbits suffering from Nagana is 
unfective. 
Laperiment 23. 
March 20, 1908.—A rabbit which was inoculated on the 7th February, 1908, with 
Trypanosoma brucei, was killed to-day in an advanced stage of nagana. On microscopical 
examination of the peripheral blood and blood from the heart, no trypanosomes were 
seen. Portions of the heart, lungs, liver, spleen, kidneys, and bone-marrow were pounded 
up in a mortar with 1 per cent. sodium citrate in normal saline. The resulting emulsion 
was then filtered through a Berkefeld filter, and 1 c.c. of the filtrate injected sub- 
cutaneously into each of two white rats. 
April 30, 1908.—Both rats healthy. No trypanosomes have appeared in their blood. 
EHapervment 26. 
ot 24, 1908.—Rabbit inoculated with 7. bruce? on 26th March, 1908. Same proce- 
dure as in Experiment 23. 
May 21, 1908.—Both rats healthy. 
Experiment 35. 
March 31, 1908.—Rabbit inoculated 7th February, 1908. Same procedure as in 
Experiment 23. 
May 4, 1908.—Both rats healthy. 
Experiment 51. 
January 31, 1908.—Rabbit inoculated 10th January, 1908. Same procedure as in 
Experiment 23. _ 
March 25, 1908.—Neither rat showed trypanosomes at any time in its blood. 
Experiment 53. 
February 3, 1908.—Rabbit inoculated 10th January, 1908. 
March 30, 1908.—Result negative. Both rats healthy. 
Conclusion. 
From these five experiments it would: appear that the blood or organs 
of rabbits suffering from nagana does not contain ultra-microscopical forms: 
of 7. brucet. 
