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what turbid, but never purulent. The vessels of the brain do not show any appreciable abnormality, but there may be a marked congestion of the arteries and veins of the dura mater. The cerebro-spinal fluid may be slightly turbid. but seldom in excess. The ventricles are never dilated and the ependyma is not granular. The brain substance is of normal consistence and the convolutions are neither flattened nor wasted. Puncta cruenta are rarely marked in the cut surface of the cerebrum. The medulla shows to the naked eye marked congestion of the vessels: In one of Mott’s cases the roots of the cauda equina were surrounded by a gelatinous yellow deposit.
_ The microscope shows the pia-arachnoid infiltrated with small round nucleated cells; the inflammation is seen throughout the whole central nervous system, but especially in the medulla and at the base of the brain. Tt can be traced along the blood-vessels and septa into the substance of the nervous system. The perivascular lymphatics around both large and small vessels are crowded with these lymphocytes. The cells of the cerebral cortex show a normal outline, but scattered through the substance, especially in the pericellular Spaces, are the small round nucleated cells. _The enlargement of the lymph glands throughout the body, and the enormous accumulation of lympho- y within the perivascular lymphatics of the ferebro-spinal system, indicate that the specific agent sleeping sickness is essentially a parasite of the tics, but that it is capable of damaging the elements, either by mechanical action, or,
ossibly, by elaborating a special toxine,
EPIDEMIOLOGY.
The epidemiology of sleeping sickness is as yet very Hectly known, but it presents several remarkable arities, The ‘disease is strictly connected with
THE JOURNAL OF TROPICAL MEDICINE. 203
water. It prevails along rivers and streams or on the shores of lakes. Several people have remarked that its endemic centres correspond as a rule with the worst malaria stations, and Corre lays special stress on the paludal nature of the sleeping sickness centres of Joal and Portudal in Senegambia. In Uganda, where it has only just appeared, it is confined to the northern shores of Lake Victoria Nyanza and to the adjacent islands. Another characteristic feature is its patchy distribu- tion. The disease is not generally diffused throughout a river valley or other endemic district, but affects particular foci, clings to particular villages, and is not observed in places near by. Corre has frequently remarked that sleeping sickness may attach itself to a particular house or to a particular group of houses. It may suddenly appear in villages hitherto immune and cling to the place for years. As to season, the only information is that of Corre, who states that in Sene- gambia a number of patients believed they had con- tracted the disease during the rainy season. Neither age nor sex seems to have any special influence. Sleep- ing sickness may make its appearance at any epoch of life, but it is more commonly found between the ages of 12 and 20 years. It is very rare at an earlier age than 3 years, but this does not prove a protective influence of the period of lactation as conjectured by Ziemann and others. Males and females are equally affected. O_p THEORIES.
Various theories have been put forward at different times to account for this strange and formidable disease. Some believed it to be a kind of nostalgia intensified by the ill-treatment suffered at the hands of slave- dealers and planters. Other equally irrelevant theories are those which ascribe the disease to malaria, to sun- stroke, to sorcery, to the immoderate drinking of palm- wine, or to the smoking of Indian hemp.
Corre, in his first paper on sleeping sickness, con- jectured that the disease might be a kind of food poison- ing analogous to ergotism and lathyrism, but later he put it down to scrofula on account of the frequent occurrence of glandular swellings. Calmette, in 1888,” compared the disease to pellagra, and Ziemann” revived again last year the food-intoxication theory by ascribing sleeping sickness to the eating of raw or unsuitably prepared manioc. Ziemann says that he was led to this theory by a previous study of pellagra and beri-beri, which, he affirms, are known to be diseases of intoxica- tion. But so far no one has actually proved that pellagra is caused by some specific toxic substance contained normally in maize, neither has anyone proved that beri-beri is due to the consumption of rice. Both maize and rice are perfectly healthy foods under ordinary conditions, and whatever their part may be in the natural history of p2llagra and beri-beri, they certainly do not stand in the direct relation of cause and effect. Like many other food-plants now extensively cultivated in West Africa, the bitter cassava (Manihot utilissima) and the sweet cassava (Munthot aipi) were imported from South America. The areas of their cultivation and consumption in Africa do not in any way coincide with the geographical distribution of sleeping sickness. Another reason against the food theory is the occur-