662 

restricting their destruction in ‘Fly Country” be 
removed, but active measures should be taken for 
their early and complete blotting out. It must be 
strictly borne in mind that this only refers to wild 
animals living in “‘fly”’ areas. No pathogenic try- 
panosomes have up to the present been found by the 
Commission in the blood of animals living in fly-free 
areas. 
(2) T. gambiense, the Parasite of Congo Sleeping- 
Sickness.—T. gambiense (Fig. 4) is very similar in 
size and shape to T. brucei, but it would appear to be 
possible to distinguish them by the presence of the 
blunt-ended, posterior-nucleated forms which are so 
common in the blood of animals infected by the 
nagana parasite and quite absent in animals infected 
by the other. But as these posterior-nucleated forms 
are absent or scarce in the blood of man, this method 
of diagnosis requires the inoculation of experimental 
animals and the study of many preparations of their 
blood. It would appear to be impossible at present to 
distinguish between the two species by the micro- 
scopical examination of preparations made from the 
blood of man alone. 
SUSCEPTIBILITY OF ANIMALS TO T. gambiense. 
A marked difference exists between T. gambiense 
and T. brucei in regard to their virulence towards 
animals, 

Py OR oH BR fin a 
MA NG NG lo on ! 
Bee ate a) oat) 
iN res ee 
( ee 






ry 


Fic. 4.—T7rypanosoma gambiense (Dutton). 
xabout 700. 
Tanganyika, 1913. 
It is almost impossible at first to give this disease 
to goats, monkeys, dogs, and guinea-pigs. The rat 
is the animal which is least refractory. 
Taste III].—Showing the Average Duration in Days 
of the Disease caused by T. gambiense, Tangan- 
yika, compared with that caused by T. brucei, 
Zululand, 
Monkey 
Dog  Guinea-.ig White rat 
T. gambiense 159 96 264 137 
T. brucei 26 34 67 30 
The disease in animals caused by T. gambiense is 
thus much more chronic than that caused by T. brucei, 
and this character, combined with the morphology 
already described, affords the surest and safest means 
of separating these species. 
G. palpalis THE CarRiER OF T, gambiense. 
Inrecrivity or Witp G. palpalis. 
In 1903 at Entebbe, the Government cantonment, 
the tsetse-flies had plenty of opportunity of becoming 
infected, since they were caught in the vicinity of 
the hut-tax labourers’ camp. These men came in 
thousands to Entebbe to work for Government for 
one month in lieu of paying hut-tax. They lived in 
NO. 2389, VOL. 95] 
NATURE 

[AuGusT 12, 1915 

rudely-built grass huts near the lake shore, and on 
examination of their blood some 30 per cent. of them 
were found to harbour the parasite. In 1903, while 
these highly-infected labourers were living on the lake 
shore, the proportion of infective flies was found to 
be as high as 11-2 per 1000. The Government removed 
the hut-tax labourers from the vicinity of the lake, 
which became deserted, and a year afterwards the 
proportion of infected flies fell to 1-2 per rooo. When 
the Commission returned to Uganda in 1908 and took 
up camp at Mpumu at the north end of Lake Victoria 
we found the lake-shore flies in the vicinity still 
infective, although the population had been removed 
early that year. The examination of 7200 flies gave 
a proportion of 1-8 per 1000. But we had given the 
Government to understand that as soon as the natives 
were removed the flies would become harmless. It 
was therefore important to find out how long the 
lake-shore flies remained infective, and why they re- 
mained infective. For this purpose they ‘were 
examined every year until 1912. 
Tas_E 1V.—Showing the Results of Yearly Examina- 
tions of wild G. palpalis from 1903 to 1912 inclusive. 


| Number of | Numberof | Proportion of 
Year.| Locality | flies flies infective flies | Remarks. 
| examined. infective per 1000 
1903 | Entebbe. 2 I1'2 _ 
1904 3) 2 ? ia — 
1908 | Mpumu. 7,200 Ir 18 tin 654 
1909 - 18,691 7 o'4 I in 2670 
1910 ” 27,179 4 o'14 1 in 6795 
IQIL “A 23,899 I 0'04 1 in 23899 
Igt2 “A 28,279 4 org 1 in 7070 




From this it will be seen that although there had 
been a steady decrease in the proportion of infective 
flies, a few remained, and these showed no sign of 
disappearing. The mistake made by the Commission 
was first in believing that the transmission of the T. 
gambiense was mechanical, and that a fly lost its 
power of infection within three days after feeding on 
an infected animal; and, secondly, in believing that 
man was the sole reservoir of the virus. It was found 
that a fly may remain infective for several months, 
and that man is by no means the only source of the 
Virus. 
THE CycLe or DeveLopMENT oF T. gambiense 1N 
G. palpalis. 
This prolonged infectivity which some flies possess 
is due to the fact that in these the trypanosomes do 
not die off, but proceed to further multiplication. It 
was shown that a very small proportion of flies which 
feed on an infected animal show this cycle of develop- 
ment. In one series of experiments, forty-two in 
number, only one fly in 212 (0-5 per cent.) became 
infective. An average of thirty-six days is required 
to complete the cycle. The long account given may 
be summarised as follows. 
Trypanosomes taken into the alimentary canal of 
tsetse-flies retain their shape and infectivity for some 
eighteen hours. They then degenerate and lose their 
power of infection, and as a rule have disappeared 
altogether from the majority of the flies by the fifth or 
sixth day. In a small percentage of flies, male as well 
as female, the trypanosomes maintain their position, 
they continue to multiply, and in a short time swarm 
in the alimentary canal of the fly. These multiplica- 
tion forms bear little or no resemblance to the original 
trypanosomes. After some twenty or thirty days the 
developing flagellates find their way into the salivary 
glands, resume their original blood form, and regain 
their infectivity. 

