316 REPORT OF THE HARVARD AFRICAN EXPEDITION 
performed with the trypanosome of horses and mules, have been made. The 
subject of animal trypanosomiasis is discussed in Chapter XX VII, page 448. 
Diagnosis. In many eases of human trypanosomiasis, in contradistinction 
to many cases of animal trypanosomiasis, it is exceedingly difficult to find try- 
panosomes in the blood. While the number of trypanosomes is subject to 
fluctuation, it, however, is true that exceptionally in trypanosomiasis in animals 
the parasites are rare in the blood, and, on the other hand, occasionally in try- 
panosomiasis of man, are plentiful in the blood. As an example of the latter 
condition, Connell ! has recently called attention to the unusually large numbers 
of trypanosomes that were present in a single human case, sometimes as many 
as three or four being seen in the oil immersion field. Kleine * has also very re- 
cently seen human cases where the trypanosomes were numerous in the peripheral 
blood. Nevertheless, it is a well-known fact to those who are familiar with 
sleeping sickness in man, that in human beings as a rule there is difficulty in 
demonstrating trypanosomes in the circulating blood. This fact was especially 
emphasized to us on the present Expedition and we soon found the futility of 
making microscopical examinations of the blood for the diagnosis of many of 
the human cases of trypanosomiasis. In many instances, puncture of the slightly 
enlarged cervical lymphatic glands, and low power microscopical examination of 
the gland juices from the end of the hypodermic needle used for puncture, will 
reveal the presence of trypanosomes by their movement, when they cannot be 
found in the blood. Even in material from the glands, however, the number of 
trypanosomes may be exceedingly small and a search of an hour or more may 
be necessary before a single parasite is seen. 
Some of the native microscopists in the Belgian Congo have become wonder- 
fully skillful in the diagnosis of trypanosomiasis by microscopical examination. 
They usually make use of a low power objective and search first for movement 
among the red blood corpuscles, such movement suggesting the presence of 
trypanosomes, and they will occasionally find one after an hour or more of 
search and demonstrate it. 
The trypanosomes are so very scanty in the blood as a rule that there is only 
a chance of finding them in fairly large numbers in advanced cases of the disease 
after centrifugation, when they sometimes also may be found in the centrifuged 
cerebral spinal fluid. 
Prevalence. With reference to the distribution of sleeping sickness in Africa, 
it still prevails in the Belgian Congo, particularly in the Kwango, Kasai, and 
Semliki districts. Thus in the Belgian Congo, Schwetz * reports in the Kwango 
and Kasai districts, that 45,000 cases were detected in a population of 550,000. 
In the French African territory, G. Martin ‘ in the examination of a half million 
inhabitants found 28,500 cases, or about five per cent of infection in the popu- 
lation. Blanchard and Laigret ° reported in 1926 that the disease particularly 
1 Connell: Tanganyika Territory Ann. Med. & Sanit. Report (1926), p. 112. 
® Kleine; Final Report, League of Nations Intern’l Commission on Human Trypanosomiasis. Geneva 
(1928), p. 9. 3 Schwetz: Bull. Soc. Path. Exot. (1924), XVII, 76. 
4 Martin, G.: Trop. Dis. Bull. (1924), X XI, 50. 
* Blanchard and Laigret: Ann. Méd. et Pharm. Colon. (1926), XXIV, 67. 
