TO SOME DISEASES OF STOCK 
893 
develop in the proboscis. A second group develop in the 
intestinal tract and the proboscis, and do not invade the 
salivary glands. To this group belong those forms commonly 
found in stock, and which are capable of infecting cattle, 
horses, dogs, and small animals of the laboratory — such as 
rats and rabbits. 
A third group develop only in the proboscis, never in the 
intestinal tract. The trypanosomes of this group are peculiar 
not only in this mode of development, but also in their micro- 
scopical appearance in the blood of infected animals, and from 
the fact that they will not affect dogs, rats, and rabbits, and are 
primarily disease-producers in cattle, much more rarely of horses. 
By the dissection and examination of wild tsetse-flies, 
therefore, it is possible to form an idea of the class of trypano- 
some to be encountered in a given locality, and an indication 
of the practical application of this is offered by the recent 
operations in German East Africa. Had a pre-war survey 
been possible, enormous saving of animal life might have 
been effected. 
It must not be forgotten, however, that a tsetse-fly may 
become infected with more than one species of trypanosome — 
a fact that would complicate the diagnosis by dissection alone, 
but which also finally dispels the view that one species of 
fly carries only one species of trypanosome. 
In this Protectorate we have found about ten species of 
trypanosome, the identification of which is made on the main 
grounds of (1) microscopical appearance, and (2) effect upon 
animals. 
By the microscopical appearance, we can readily dis- 
tinguish a small form of only 10 to 15 micron from a giant 
form of 50 to 70. Some trypanosomes possess a long free 
flagellum ; in others this is absent. In some the undulating 
membrane is much better developed than in others ; and in 
one species a small and characteristic nuclear body, which 
occurs in all others, is missing. 
So by the effect upon animals. There is a group which will 
not infect dogs and laboratory animals — e.g. rats, guinea-pigs, 
and rabbits ; and of this group, most of which can affect cattle 
and sheep, are species which will not produce disease in horses 
