394 
Have Trypanosomes an Ultra-microscopical Stage in their 
Infe-history ? 
By Colonel Davip Brucz, C.B., F.R.S., Army Medical Service, and Captain 
H. R. BATEMAN, Royal Army Medical Corps. 
(Received June 6,—Read June 25, 1908.) 
By an ultra-microscopical stage in the development of a micro-organism 
is meant a stage in which the parasites are so small as to be invisible to 
the highest powers of the microscope, and to be capable of passing through 
the pores of a porcelain filter. For example, a drop of South African horse- 
sickness blood will give rise to the disease if injected under the skin of a 
healthy horse. If a similar drop is examined under the highest available 
powers of the microscope, nothing in the shape of a micro-organism can be 
seen. If this blood is filtered through a porcelain filter, the virus passes 
through, and the filtrate is found to be as infective as the original blood. 
Horse-sickness is therefore looked upon as a disease caused by an ultra- 
microscopical micro-organism. | 
For some time it has been reported by various workers that an ultra- 
microscopical stage exists among the trypanosomes. For example, Plimmer 
informs us that he found the filtered blood of nagana animals to be infective. 
Salvin Moore and Breinl write that the blood of animals suffering from 
Trypanosoma gambiense infection, although apparently containing no trypano- 
somes at all, and even if properly filtered, is still capable of infecting other 
animals into which it may be introduced. MacNeal also makes a similar 
statement in regard to Trypanosoma lewisi. He states that “in culture, on 
blood-agar, 7. lewisi may give rise to much smaller forms, and that such 
cultures, after passage through a Berkefeld filter, still infect rats.” Finally, 
it may be noted that the late Dr. Fritz Schaudinn, whose too early death 
we all lament, expressed the belief that trypanosomes may multiply by 
longitudinal division so rapidly as to become small enough to pass readily 
through a Chamberlain filter. 
This subject is an important one, as the discovery of an ultra-microscopical 
stage in these trypanosomes might throw light on the causation of some 
diseases in which no parasite can be found. In kala-azar, for example, the 
intra-corporeal form is small, and the extra-corporeal a fairly large flagellated 
organism. Let us imagine that the Leishman body lying inside the splenic 
cells had still further subdivided and become ultra-microscopical, then we 
would have an invisible parasite causing a serious disease in man and 
