44 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
Heads and probosces of the tsetse flies and stomoxys used in these experiments 
were frequently dissected. In none of them were trypanosomes, as they are observed 
in the blood, ever seen. The head parts of insects were examined immediately after 
they had fed upon animals in whose blood the parasites were exceedingly numerous, 
and never were'they found to contain recognizable trypanosomes either living or dead. 
Living actively motile parasites, not in the least degenerated, were, however, 
seen in the stomachs of these flies for many hours after their ingestion. Their 
peculiarities and the alterations which they later underwent will be considered in a 
further report. 
Our fly experiments were done during the dry season. It is possible that 
they failed owing to the excessive lack of moisture which could not fail to have made 
it impossible for the parasites to live, for even a few hours, in the insect's proboscis.* 
An observation, interesting in this connection and based upon a very careful 
diary, has been related to us by Mr. Hewby, F.R.G.S., formerly a resident in 
Northern Nigeria. 
There is on the north bank of the river Benue (Nigeria), opposite Ibi, a 
notorious tsetse fly belt where Glossina occurs and in which horses contract ' tsetse 
fly' disease. 
Mr. Hewby unhesitatingly picked out specimens of Glossina palpalis from 
our collections, and assured us that the tsetse fly of Ibi was practically identical with 
them. The symptoms and duration — three to (rarely) ten weeks — of the disease in 
horses (it also affects cattle) convinced us that what is called tsetse fly disease in 
Northern Nigeria is most probably Nagana. 
On two occasions (1899-1900) all the horses sent by Mr. Hewby and others 
through this particular ' belt' during the rainy season contracted 'fly disease ' and 
died. 
Twice during the dry season (1901-1902), although the tsetse flies — seen 
also during the wet season — were extremely numerous, have ponies gone through 
the same belt of fly-bush without suffering harm. Once a pony taken in the dry 
season (May 1 902) through a bit ot bush comparatively near the Ibi belt ' was 
covered for hours ' with the fly and yet did not contract the disease. 
Mr. Hewby also informed us that, as in the Gambia, the neighbourhood of 
the river is believed in Nigeria to be unhealthy for cattle and horses during the rains. 
It is in addition generally believed that the fly is practically harmless during the dry 
season. It is interesting- to note that Mr. Hewby knows of no instance in which 
asses and sheep have suffered from ' fly-disease.' 
* At McCarthy Island, during the period at which our Stomoxys experiments were done, the dry thermometer in our 
laboratory daily registered about 95° F., the wet bulb thermometer being usually from 15 0 to 20 0 lower. 
Though the conditions were similar during the tsetse fly experiments done at Cape St. Mary the temperature was nut so 
hieh nor was the daily difference between the wet and dry bulb thermometers so great. 
