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one would be inclined to consider them quite distinct 
did one not know their origin. 
3. Immunity. —The best test of the difference 
between two trypanosomes lies, perhaps, in the fact 
that an animal immunized against one trypanosome 
will yet succumb to another, e.g., Laveran and Mesnil 
base their belief in the non-identity of Ngana and 
Surra on the following fact. A goat or cow recovered 
from 7 . brucei infection is inoculated again with 7 . 
brucei. No effect is produced, and its blood in several 
c.c. is not infective for other animals. It is now 
inoculated with 7 . evansi , and its blood becomes 
infective even in a few drops. It cannot here be a 
question of difference of virulence of different strains, 
for 7 . brucei is as virulent as 7 . evansi for cattle. 
Again, mice infected with 7 . equinum and cured by 
Trypan-red or arsenic are susceptible to 7 . equiperdum , 
and when cured of 7 . equiperdum mice are susceptible 
to 7 . brucei. 
4. Precipitin 7 est. —Mayer added to the serum 
of a dog infected with 7 . brucei the salt extract of 
centrifugalised 7 . brucei trypanosomes. A copious 
precipitate resulted. With the serum of a dog infected 
with 7 . equinum , he got no result. 
Agglomeration of Trypanosomes 
Under various conditions trypanosomes come 
together and form rosettes, sometimes of about a 
hundred individuals. In these the posterior ends are 
central, united by a slimy secretion derived from the 
blepharoplasts (?), and the flagella are peripheral. They 
may be seen in the peritoneum after injection by this 
path. Chemical reagents, immune sera, and also 
normal sera, are in particular cases capable of producing 
