470 G-ENEEAL DISEASES. 



with a high daily temperature. Deep kloofs or gullies where 

 vegetation is abundant and the ground, below the undergrowth, 

 moist, are especially dangerous to susceptible animals. Dry, high 

 pastures at an altitude, say, of 6,000 feet above the level of the 

 sea, are as a rule free from the disease, unless they have been 

 contaminated by the introduction of aflected stock ; the original 

 liome of this organism appearing to be moist and low-lying lands. 

 Many of the South African highlands, which were formerly exempt, 

 have become infected, apparently by the introduction of diseased 

 horses. At present it is not possible to say how long the microbes 

 of horse sickness would continue to exist in a dry and cold locality, 

 in which they would be more or less exotics. Remarks as to the 

 prevalence of horse sickness at Johannesburg, show that any pre- 

 ventive effect which altitude above the level of the sea may have 

 on horse sickness, is due to increased cold and dryness. In almost 

 all cases, frost stops the progress of an outbreak of horse sickness. 



Practical observations and the elaborate bacteriological researches made 

 by Edington, leave no doubt that this disease is caused by a microbe which, 

 like that of rabies, has not yet been isolated. We have, however, suflBcient 

 proof to reasonably assume that this organism, whatever it may be, becomes 

 developed into a virulent condition on grass and other herbage, under the 

 combined influence of heat and moisture. It is probable that the microbe 

 of horse sickness (supposing that such an organism exists) forms toxins 

 which exert a paralysing action on the vaso-constrictor nerves, and thus 

 causes dilation of the blood-vessels, with consequent increase in the amount 

 of plasma exuded into the tissues, and has also a poisonous effect on the 

 system. " Horse-sickness appears to be a septicsemia in the further sense 

 that death is due to the toxic effects of substances manufactured by the 

 bacteria multiplying in the blood. No doubt in those cases in which there 

 is very extensive pulmonary oedema, interference with ■ the aeration of the 

 blood will act as a contributory cause of death, or it may be the final cause ; 

 but in a considerable number of the experiments recorded in this article, the 

 combined structural lesions, such as the cedema of the lungs and the 

 exudation into the pleural and pericardial sacs, were not sufficient to account 

 for the fatal issue. It ought also to be noticed that the microbe of horse- 

 sickness does not appear to attach itself to the red corpuscles of the blood ; 

 at least, that seems to be indicated by the fact that these corpuscles appear 

 quite normal in preparations made from the blood, and by the normal tint 

 of the serum furnished by horse-sickness blood " (McFadyean). This 

 eminent bacteriologist considers that it is highly probable that the agent of 

 infection in horse-sickness is too small to be made visible to the numan 

 eye, even when aided by the highest powers of the best modern microscope. 

 He supports this opinion by the fact that "horse-sickness blood is not 

 deprived of its effective property by filtration through a Berkefield or a 

 Chamberland filter," either of which might arrest some of the contained 

 bacteria ("Journal of Comp. Path.," June, 1901). 



POST-MORTEM EXAMINATION.— Throughout the course of 

 numerous post-mortem examinations one negative feature stands 

 out in remarkable prominence, namely, the almost total absence 

 of any true inflammatory phenomena ; while the conditions obtain- 



