Have trypanosomes an ultra-microscopical stage in their life-history?

By an ultra-microscopical stage in the development of 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. House-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 fromTrypanosoma gambiense infection, although apparently containing no trypanosomes 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 toTrypanosoma lewisi . He states that “in culture, on blood-agar,T. 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 Camberlain filter.