398 Have Trypanosomes an Ultra-microscopical Stage Z 
To ascertain of the Cultwation of Trypanosomes on Blood-agar will give rise to 
Ultra-microscopical Forms which are capable of passing through a Berkefeld 
ulter. 
Experiment 24.— White Rats. 
March 20, 1908.—The water of condensation from six flasks of blood-agar, upon which 
T. lewist had been planted out for 18 days, was to-day filtered through a Berkefeld filter, 
and 4 ¢.c. of the filtrate injected into two white rats. 
April 28, 1908.—These rats have remained in good health and no trypanosomes have 
appeared in their blood. 
Experiment 37.— White Rats. 
April 1, 1908.—A test-tube of blood-agar (2—1), which contained a luxuriant growth of 
T. lewist, was shaken up with 25 c.c. of normal salt solution, and the resulting emulsion - 
filtered through a Berkefeld filter. The filtrate was then injected into the peritoneal 
cavity of three white rats. 
April 30, 1908.—All three rats remained well, and trypanosomes never appeared at any 
time in their blood. 
Experiment 36.— White Rat (Control). 
March 31, 1908.—To ascertain if the culture used in Experiment 37 was virulent, three 
drops of the condensation fluid were injected into a small white rat. 
April 6, 1908.—T. lewist appeared in the blood of this rat. 
EHaperiment 64.— White Rats. 
April 9, 1908.—A blood-agar tube containing a growth of 7. lewisi, first generation, 
46th day of growth, was shaken up with normal saline and filtered in the usual way. The 
filtrate was injected intra-peritoneally into two rats. 
May 11, 1908.—Both rats well. Trypanosomes have never appeared in their blood. 
Experiment 98.— White Rats. 
May 7, 1908.—Two blood-agar tubes, 27th day of growth. Same procedure as in 
Experiment 64. 
June 2, 1908.—Both rats healthy. 
Experiment 97.— White Rat (Control). 
May 7, 1908.—To ascertain if the culture used in Experiment 98 was infective, 3 c.c. of 
the condensation fluid was injected intra-peritoneally. 
May 18, 1908.—T7. lewisi in the blood. 
Conclusion. 
From these experiments it may be concluded that cultures of 7. lewase 
on blood-agar do not give rise to ultra-microscopical forms which are capable 
of passing through a Berkefeld filter. 
The final conclusion arrived at is that neither 7. bruce nor evanse 
develop in the body of animal forms so small as to be capable of passing 
through the pores of a Berkefeld filter, and that in cultures of 7. /ewist on 
blood-agar such small forms are also absent. 
