598 
R. W. BURKE. 
ing of the nerve cells; but beyond a tendency to congestion 
and occasional blood extravasation, no lesions are usually 
discovered in the nervous system. 
I think that we may safely formulate a definition of this 
disease with the aid of the foregoing observations. It is es¬ 
sentially a blood disease allied to, if not identical with, that di¬ 
sease of mankind known as pernicious anaemia. It assumes an 
acute and a chronic form, but more frequently the latter in the 
equine species in India, and is known under a variety of 
names—intermittent and remittent fever, malaria, malarial 
cachexia, pernicious anaemia, etc.—depending on the stage 
of development and other features. That an acute form of 
surra occurs in horses was noted by many observers, and we 
have already pointed out, in Tropical Diseases of the Horse, 1888, 
p. 41, and elsewhere, that this was in fact intermittent and 
remittent fever of the horse, which is better known perhaps 
under the common name of ague, malaria, etc. And Dr. 
Ranking has recently corroborated our views, and states that 
in those cases of surra among horses in which he noted the 
presence of parasites, there was a decided likeness to malarial 
fever of mankind. 
Regarding the true nature of the parasite it will suffice 
here to state that some authorities regard it as belonging to 
the class Infusoria, a higher group of Protozoa; while others 
think it more probably belongs to the class of Mycetozoa 
(or fungus animalcules) which lie on the confines of animal 
and vegetable life. 
The parasites of surra present a remarkable complexity 
of organization, that constitutes the great difficulty of classi¬ 
fying and distinguishing species which undergo marked 
changes of form before arriving at maturity. Hence we may 
speak of them as occurring in the imperfect or juvenile form, 
and in the mature form ; and it is in accordance with analogy 
to suggest that the 1 flagellated,’ the ‘ crescent,’ the ‘ intra¬ 
cellular, the ‘ free ’ and other forms are stages in the develop¬ 
ment of the same species. 
The problem of the connection between plasmodium mala 
rice and the bacillus malarice still awaits solution. How fruit¬ 
ful such a line of investigation may be has been conclusively 
