346 
NATURE 
[FEBRUARY II, 1904 
true to-day as when Winterbottom wrote 100 years 
ago that it proves fatal in every instance. What, then, 
is the cause of this fatal disease? In order to appre- 
ciate fully the recent discovery of its nature it will be 
necessary to recall to our mind what we know of the | 
Those who 
nature of some other well-known diseases. 
are at all familiar with works of travel on Africa will 
have read of the tsetse fly and the tsetse-fly disease in 
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Fic. 1. 
cattle—ngana. Travellers well know the danger to 
their cattle and horses of the ‘‘ tsetse-fly belt,’? and 
various devices have been employed to escape the deadly 
bite of the fly, such as smearing the animals with dung 
and passing through “‘ the belt ’’ at night, when the 
flies, as a rule, do not bite, or even covering the horses 
with a suit of clothes. ; 
The deadly fly disease ngana was first elucidated 
by Col. Bruce, R.A.M.C., F.R.S., who proved that the 
disease was due, not to a poison injected by the fly, as 
Livingstone had supposed, but to a living organism, 
microscopic in dimensions, worm-like in aspect, moving 
about in the blood. This organism—a trypanosome— 
the tsetse fly introduces into the blood at the time of 
biting. It should be clearly understood, moreover, that 
the fly derives this trypanosome, not from water, not 
from decomposing matter, but solely from the blood of 
another animal containing these trypanosomes. The 
disease is, in fact, contagious just as malaria is, and 
in this case also the contagion (the trypanosome) is 
transmitted, not by contact of the healthy with un- 
healthy anim uls, but only through the agency of a fly. 
“Ngana,”’ then, is a disease in cattle caused by a 
trypanosome. ‘‘ Surra, ”» a somewhat similar disease 
well known in India, is also caused by a trypanosome, 
likewise mal de Caderas in South America. 
diseases affecting animals, but in rg02 Dutton, who 
was working in Gambia, found for the first time a try- 
panosome in man (a European). This, too, was the 
cause of a fatal disease, for the patient died in Liverpool 
about a year later. 
Trypanosomes, then, are the cause of fatal diseases in 
animals, and even in man, and in one of these—ngana 
—the mode of infection is by the bite of a tsetse fly. Let 
us now turn to recent discoveries in sleeping sickness. 
In November, 1902, 
NO. 1789, VOL. 69] 
These are 
Castellani, in Uganda, examin- | 
ing the cerebro-spinal fluid of a case of sleeping sick- 
ness, found a trypanosome. Bruce and Nabarro, who 
arrived in Uganda in March, 1903, were struck with the 
importance of this discovery and forthwith took up 
energetically an examination of the disease in this 
direction, with the result that they found trypanosomes 
in the cerebro-spinal fluid of all cases examined by 
them, and, moreover, they also found them in the 
blood. Now in all experimental work, results are fre- 
quently almost valueless unless control experiments are 
made. Consequently it was next established that the 
cerebro-spinal fluid of those not suffering from the 
disease did not contain trypanosomes. But although 
the blood of patients suffering from sleeping sick- 
ness ‘contains trypanosomes, yet they are present 
also in the blood (in 28.7 per cent. of the 
population) of natives in the sleeping sickness 
areas, but not outside these areas; a very im- 
portant fact and one which might well have 
_ escaped detection had not the control experiments been 
made. To discuss completely this fact would take us 
too far, and indeed our knowledge is still incomplete 
on this point. Suffice it to say that the existence of try- 
panosomes among the natives (not suffering from sleep- 
ing sickness) indicates cases of ‘‘ trypanosome fever,”’ 
which we have seen has been known since Dutton’s 
discovery in Gambia and which now we know to be a 
common disease among natives in certain regions, e.g. 
the Congo. Bruce and Nabarro, however, believe that 
these cases of Hye oa fever are initial cases of 
sleeping sickness. So long as the trypanosome is con- 
fined to the blood we have simply ** trypanosome fever,’ 
but when the trypanosome gains an entry into the 
cerebro-spinal fluid, then the case becomes one of sleep- 
ing sickness with the characteristic symptoms. The 
commissioners concluded, in fact, that sleeping sickness 
was due to the trypanosome. 
Now as ngana, a trypanosome disease, is transmitted 
by a tsetse fly, the question naturally arose, could this be 
established for sleeping sickness? In the first place a 
search was made for tsetse flies; they were easily found. 
In the next place, by a systematic collection of 
biting flies of all kinds from the district, it was found 
that the distribution of the disease and that of a certain 
species of tsetse fly was practically identical. In 
Fic. 2. 
fact, the tsetse fly involved (Glossina palpalis) is, like 
| sleeping sickness, practically confined to the shores of 
| Victoria Nyanza and the islands. This, then, was an 
important confirmation of the trypanosome nature of 
the disease. Further, also, it was proved by experi- 
ment that the fly could transmit the trypanosome from 
the unhealthy (sleeping sickness patient) to the healthy 
(monkey), and the monkeys succumbed, with symp- 
