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Trypanosomiasis 
to an animal harbouring the trypanosome in its blood it will be seen 
that 40 to 90 "/o of the trypanosomes no longer show blepharoplasts 
after the expiration of 24 hours from the time the drug was administered. 
In this respect the oxazine preparation is the more powerful drug. If 
such trypanosomes are now passed through a series of 10 rats, each 
rat being in turn treated with the drug, it will be seen that the 
trypanosomes acquire a great resistance to the drug and that, with time, 
they no longer show blepharoplasts. If the trypanosomes have been 
subjected to the continuous effect of the drug for longer periods the 
blepharoplasts will not be reacquired even when the trypanosomes 
are passed through a series of 130 untreated animals. The oxazine 
preparation acts directly upon the blepharoplast. In trypanosomes 
which have reacquired their blepharoplasts a change of constitution has 
been brought about, for when they are subjected to the effects of 
arsenicals or trypai’osan they again lose their blepharoplasts, this being 
contrary to what is observed in the normal flagellates. 
In other cases no appreciable alteration in morphology accompanies 
the acquisition of drug-resistance. Trypanosoma hrucei has been 
rendered resistant to parafuchsin (Francke and Roehl) and to atoxyl 
(Browning). In the latter case, this trypanosome has been found to 
remain drug-resistant during its passage through 140 untreated 
animals, this representing many generations of trypanosomes. There 
are, however, limitations to this resistance. Thus, Mesnil and Brimont 
found that T. evansi, rendered resistant to atoxyl to such a degree that 
the strain still remained resistant after passing through 110 untreated 
mice, when transferred to another host, the rat, immediately became 
susceptible to the drug whilst the rat served as its host. When the 
flagellate had passed through a series of 10 rats it was found, however, 
to be still atoxyl-resistant when returned to the body of the mouse. 
Similarly, atoxyl-resistant T. equiperdum, rendered resistant in the body 
of the donkey, has been passed successively through rats, guinea-pigs, 
rabbits and rats during a period of seven months and been found 
atoxyl-resistant upon being returned to the animal, the donkey, in 
which it was originally rendered resistant. From this we may conclude 
that atoxyl combines with a blood constituent to act upon the 
trypanosomes. When the flagellates have acquired resistance to 
atoxyl q- mouse blood, they are still susceptible to atoxyl 4- rat blood 
or other blood than that of the mouse. 
Of considerable interest, moreover, are certain observations of 
Gondei'’s (1911) upon arsenophenylglycin-resistant T. leioisi, wherein 
