roll. | Trypanosoma gambiense 17 Glossina palpalis. 527 
From the above table it is seen that the salivary glands first become 
invaded 25 days after the infecting feed. In this case the monkey did not 
become infected. This may have been due to an accident, such as this 
particular fly not biting the monkey, or the invasion of the salivary glands 
only taking place after the fiy had bitten, or to the fact that the blood-type 
of trypanosome was not present. With this exception all the other 
experiments, 12 in number, confirm the hypothesis that the fly does not 
become infective until the salivary glands are invaded. 
Another point which comes out with striking clearness is, that in all the 
salivary glands from flies which gave a positive result, trypanosomes similar 
to the short and stumpy blood-type were invariably present. 
It is to be hoped that before long the result of this work will be 
confirmed, and so added to, that the whole story of the development of 
the trypanosomes within the fly, and their passage into the salivary glands, 
will be unfolded. 
~ Conclusions. 
1. In the course of the development of Trypanosoma gambiense in 
Glossina palpalis the proboscis does not become involved, as in the case of 
some other species. 
2. A few days after an infective feed the trypanosomes disappear out of 
the great majority of the flies, but in a small percentage this initial dis- 
appearance is followed by a renewed development. 
3. After a very short time the flies which have fed on an infected animal 
become incapable of conveying the infection by their bites, and this non- 
infectivity lasts for some 28 days, when’ a renewed or late infectivity takes 
place. 
4. A fly in which this renewed or late infectivity occurs can remain 
infective for at least 96 days. 
5. An invasion of the salivary glands occurs at the same time as this 
renewal of infectivity, and without this invasion of the salivary glands there 
can be no infectivity. 
6. The type of trypanosome found in the salivary glands when the fly 
becomes infectrve is similar to the short stumpy form found in vertebrate 
blood, and it is believed that this reversion to the blood-type is a sine qué non 
in the infective process. 
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