1912.] On the Extrusion of Granules by Trypanosomes. 379 



The number of granules apparently varies in different species of trypano- 

 somes. They may also vary in size and number in the same species, e.g. a 

 strain of T. nanum, obtained from cattle, was carried on by passage through 

 gerbils. For two and a half months many of the trypanosomes contained a 

 single large granule. At the end of this period the granule became multiple, 

 and three or four could be seen ; at the same time there was a great 

 diminution in their size. It was noted that, coincidently with this increase 

 in number of granules, the virulence of the strain became greater. We 

 have found that granules are not necessarily always present in trypano- 

 somes. At present we can only generally indicate the stage at which 

 granules may develop,, and are unable to say what conditions determine their 

 appearance ; but the following details are the result of our observations : — 



T. brucei was investigated in gerbils, in which the disease was fatal in six 

 weeks, and during its course they showed at least two or three exacerbations 

 with a large number of trypanosomes in the blood, with corresponding latent 

 periods when they were absent. 



When trypanosomes first appeared in the blood, whether at the beginning 

 of the infection or after a latent period, it was observed that they did not 

 contain granules ; the latter developed about the fourth day after trypano- 

 somes were first seen, and increased in size and number. For about 24 hours 

 trypanosomes with granules were numerous. After this period, when free 

 granules were numerous in the blood, the proportion of trypanosomes 

 containing granules steadily diminished, till finally, though an enormous 

 number of trypanosomes might be present, granules could not be found in 

 any of them. This condition usually preceded a latent phase, or the death 

 of the animal. 



We have thus a definite sequence of events during an exacerbation of the 

 disease : — 



(1) Trypanosomes without granules. 



(2) Trypanosomes showing granules which gradually become larger and 

 very evident. 



(3) Many free granules. 



(4) Many trypanosomes but no contained granules. 



(5) Trypanolytic crisis, or death of the animal. 



This was also found to hold good with T. nanum and T. evansi (Sudan). 



In the case of a goat inoculated with T. brucei, which lived for 133 days, 

 and whose blood from the end of the first fortnight was always infective, no 

 trypanosomes were at any time discoverable in the blood, which was 

 examined daily for the first two months of the illness. In all the specimens 



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