36 HORSE-SICKNESS IN SOUTH AFRICA. 
On the other hand I can hear of no well-authenticated case 
of horse-sickness occurring in a horse fed exclusively on dry 
food—such as forage, mealies, &c.—no matter how bad the 
situation of the stable, nor how deadly the season for it. In 
all cases that have occurred in horses kept, as a rule, under 
these conditions—where I have been able to obtain reliable 
information—I have invariably found that they have either 
been allowed to graze on some occasion when out, or have had 
grass given to them in the stable; generally when they have 
been away from home or forage was not obtainable. 
The places most favorable for it are valley and low lying 
lands, but it also occurs on land at an elevation of several 
thousand feet above the level of the sea. 
In some of the most elevated districts of the Colony I 
understand that it has either never been known or only in 
exceptionably bad seasons. 
Predisposing Causes . 
Among the predisposing causes of this disease are change 
of climate, a plethoric condition from good feeding without 
sufficient exercise, and the proper regulation of the diet; a hot 
and moist atmosphere favours its development; it is depress¬ 
ing, the textures of the body are relaxed, the circulation is 
languid, and the skin as well as the lungs and other organs 
are less active in the performance of their several functions, so 
that respiration, digestion, and other vital phenomena, as 
well as the formative and eliminative processes, are impared, 
and serious results follow. 
The bad sanitary arrangements to which horses are subject 
in this country, as well as the sudden changes of temperature, 
and fatigue from severe or prolonged exertion, are also pre¬ 
disposing causes. 
After carefully considering the matter, I am led to believe 
that miasma is not the cause of the disease, but that the 
poison is contained in the grass. In support of this I may 
state that as the late summer was an unusually dry one, the 
swamps and valleys became dry, instead of being saturated or 
covered with water as usual, consequently they were in a more 
favorable condition to throw off malarious exhalations than 
usual, the effect of which was seen in the increase of fever 
among human beings; and yet the season was remarkably free 
from horse-sickness until we had rain. 
It seems to me, therefore, that heat and moisture are 
essential for the production or development of the agent which 
gives rise to this disease. What the precise nature of that 
agent is is still matter for investigation, but I think it is 
