26 
THIRTEENTH REPORT. 
Briefly stated, the trypanosomes are free-swimming parasites found in 
the blood plasma of vertebrates. They possess a nucleus, micro-nucleus, 
undulating membrane and a free flagellum. It is by aid of the undu- 
lating membrane and the whip that the parasites are able to move about 
epuite freely in the blood of the host. 
Up to ten or twelve years ago the number of known trypanosomes was 
rather small and about the only available representative was that found 
in the common wild rat. The Trypanosoma lewisi of the wild rat was 
therefore selected for experiments having for their object the development 
of a method of cultivation. With the aid of Dr. MacNeal this was ac- 
complished. in 1903, and since then the blood agar method of cultivating 
flagellates has been widely and most successfully employed. This method 
has been found especially applicable in the study of the trypanosomes 
which are not markedly pathogenic, such as those found in birds, fish, 
amphibians, insects and some mammals. Of the pathogenic forms Tr. 
brucei, the cause of nagana or the tsetse-fly disease of South Africa, is 
the only one which has been carried through a series of artificial cul- 
tures. Much effort has been expended to bring under cultivation the 
parasites causing the diseases known as Surra, Dourine, Caderas, Human 
Sleeping Sickness, etc., but without satisfactory result. It is reasonably 
certain, however, that before long the difficulties will be overcome and 
that all of these parasites will be known in their cultural forms. 
The importance of the cultural method in the study of trypanosomes 
is no less than in that of bacteria, moulds, yeasts, etc. In the first place, 
it enables the worker to detect the presence of a flagellate, even when 
it is present in such small numbers as to escape observation by the 
microscope. We have shown this to be true for the blood of birds and 
rats. During the past year a number of observations in different parts 
of the world have been made demonstrating the presence of trypanosomes 
in the blood of cattle, though none could be detected by other means. 
Another advantage of the cultural method is that it affords additional 
means for the differentiation of species. The cultural characterists may 
vary considerably, as in the case, of bacteria, and hence this feature 
is one which may assist in the identification of the blood forms. The 
trypanosomes as found in the blood of different animals often present 
only slight differences in form or size, and specific names are only too 
often given because of the mere fact that the hosts are unlike species. 
In the case of birds, we have shown that the same cultural trypanosome 
may be found in very different species and what is more important that 
a given bird may be infected with two, culturally very different kinds 
of trypanosomes. The failure to recognize these important facts have 
led observers such as Boson busch and Mayer to erroneous conclusions 
regarding the parasites cultivated from owls. The flagellates which are 
present in the gut of insects, growing as they do upon dead material, 
must be regarded as cultural forms. This view is supported by the fact 
that when such organisms, for example those found in the mosquito, 
are cultivated in the test-tube they present essentially the same char- 
acteristics. 
A further application of the cultural method is evident in connection 
with problems of immunity. It was because of the availability of pure 
bacterial cultures that so much has been done in recent years in experi- 
mental immunization to disease, and it is reasonable to believe that 
