NovEMBER 15, 1906| 
NATURE 
57 
mysterious malady until quite recently, when it made 
its appearance in epidemic form in Uganda, producing 
an enormous mortality among the natives, and also 
attacking Europeans. The outbreak of the disease 
was so serious and threatening that, at the request 
of the Government, the Royal Society sent out a 
commission to. investigate the nature of the disease, 
and to discover, if possible, the means of checking 
the further spread of the epidemic. The commission 
was not long in obtaining important results. It was 
discovered that the cause of the disease was a try- 
panosome which in the early stages of the malady 
was present in the blood of the patient, but which 
later penetrated into the cerebro-spinal fluid, and then 
gave rise to the comatose symptoms characteristic of 
the disease. It was further proved, once again by 
Bruce, that the parasite was transmitted from sick 
to healthy persons by the local species of tsetse-fly, 
Glossina palpalis, and that the sleeping sickness was, 
in fact, a human tsetse-fly disease comparable to the 
nagana of cattle, though caused by a different species 
of trypanosome transmitted by a different species of 
tsetse-fly, and differing further from nagana in the 
nature of the symptoms produced. It remained to 
investigate the exact relation of the parasite to the 
fly, that is to say, whether the trypanosome went 
through a developmental cycle in the tsetse-fly or 
not. It may be added that in the case of sleeping 
a h c 
Fic. 1.—/7yfanosoma ganibiense from the intestine of the tsetse-fly, 
twenty-four hours after feeding upon an infected subject. @ and 4, 
male forms ; ¢ and a, female forms. x 2000 diameters. 
sickness no natural ‘ reservoir ”’ 
covered. 
Early in 1905 the present writer was sent out to 
Entebbe by the Royal Society in order to investigate 
the exact nature of the relationship between the 
trypanosome of sleeping sickness, T. gambiense, 
Dutton (=T. castellanii, Kruse), and the tsetse-fly 
Glossina palpalis. At the time of commencing this 
work the state of knowledge was as follows :—The 
experiments of Bruce and Nabarro had proved that 
the tsetse-fly was capable of transmitting the para- 
sitic micro-organism from an infected animal to one 
free from the infection if fed on the first, then on 
the second, with not more than forty-eight hours’ 
interval; and, further, that tsetse-flies freshly caught 
in localities where sleeping sickness is rife, such as 
Entebbe, were capable of infecting healthy animals. 
Trypanosomes had also been observed to be present 
not infrequently in the digestive tract of freshly- 
caught flies, occurring in enormous numbers in 
certain regions of the intestine. Special interest 
attached, naturally, to these ‘“‘ wild’’ trypanosomes, 
as they may be termed briefly, meaning thereby 
trypanosomes with which the fly had become infected 
in nature, and not as the result of being fed in the 
laboratory on infected animals. Lieuts. Gray and 
Tulloch, of the sleeping sickness commission, had 
NO. 1933, VOL. 75] 
has yet been. dis- 
made detailed observations on the wild trypanosomes, 
and had found them present in about 1-8 per cent. 
of tsetse-flies caught at Entebbe. The wild trypano- 
somes differed considerably in appearance and struc- 
ture from those found in the blood or cerebro-spinal 
fluid of sleeping-sickness patients, but not more than 
was capable of being explained as the result of 
developmental changes. 
At that time the late Dr. Fritz Schaudinn had just 
published his wellknown memoir on the life-cycle 
of the trypanosome of the little owl, Athene noctua, 
a work which created considerable stir among all 
workers upon Protozoa. We were, therefore, all fully 
prepared to discover complicated life-cycles involving 
great morphological changes in these organisms, and 
had little doubt but that observation would reveal a 
developmental cycle in the tsetse-fly analogous to 
that of the malarial parasite in the mosquito. It was, 
moreover, reasonable to suppose that the trypano- 
somes found in tsetse-flies caught in Entebbe would 
be the trypanosomes of sleeping sickness, since, as 
already stated, it had been proved experimentally that 
infection could be brought about by the bites of 
freshly-caught flies. When, therefore, we—that is, 
the present writer working in collaboration with 
Messrs. Gray and Tulloch—embarked upon these in- 
F1G. 2.—Trypanosoma grayi from the intestine of the tsetse-fly. a, male 
4, female ; c, indifferent ; and @, young forms. 2000 diameters, 
vestigations, we were fully convinced that the wild 
trypanosomes found in the tsetse-fly were nothing 
more than stages in the developmental cycle of 
Trypanosoma gambiense, and that it remained to 
work out this cycle in full detail and to refer the 
various forms of wild trypanosomes to their place 
in it. 
The methods by which this problem was attacked 
were partly experimental, partly observational. By 
both alike, all attempts to establish a relationship 
between Trypanosoma gambiense of sleeping sick- 
ness and the wild trypanosomes occurring naturally 
in the tsetse-fly gave absolutely negative results, and 
forced us gradually and reluctantly, but irresistibly, 
to the conclusion that the wild trypanosomes of the 
tsetse-fly have no connection whatever with sleeping 
sickness, but belong to other species quite distinct 
from T, gambiense, and innocuous to man. 
One series of experiments had for its object to 
determine the exact manner in which the tsetse-fly 
carries the trypanosome of sleeping sickness from an 
infected to a healthy animal. If the parasite passed 
through a developmental cycle in the tsetse-fly, it 
might be expected that the latter would show a certain 
periodicity in its infectiveness; that is to say, that 
