ON HYDATIDS IN THE SHEEP. 
52 J 
weakly sheep ; or, under certain conditions of the brain, are these 
entozoa produced spontaneously ? and if so, what are the laws and 
the conditions of their production ? Has a state of debility any 
influence on the production of these parasites? or why should 
their appearance be confined to the very youth of the animal? 
Of these things I know nothing—they are mysteries which I am 
unable to penetrate; but the mode of reproduction in the hyda¬ 
tid I know, and it is singular enough. Smaller hydatids are 
found floating in the belly, if we may so term it, of the larger 
ones. Many dozens of them have occasionally escaped when the 
parent has been wounded, and on the rugous surface of the enve¬ 
lope of the hydatid, and particularly towards the neck of it, 
there are numerous minute granules or vesicles, which are 
probably the germ of future hydatids, while on the outer coat of 
the hydatid there are certain irregularities, little points or granu¬ 
lated projections, by means of which the hydatid seems to be 
united to the cerebral substance. 
Progress of the Disease .—These parasitical animals are pro¬ 
bably exceedingly small when first deposited in the brain; and 
whether their growth is slow or rapid, they at first produce little 
disturbance there—no altered function will tell of their presence : 
but when they have attained a considerable bulk, and press upon 
the neighbouring vessels, or the origins of the cerebral nerves, 
their presence cannot be mistaken. 
If the head should sometimes be held on one side and some¬ 
times on the other, it indicates that there is an hydatid in each 
lobe of the brain. In a very few cases the sheep will march 
straight forward, with his head depressed* running against every¬ 
thing in his way, and continually falling: the hydatid will then 
be found to be attached to the corpus callosum, and to occupy 
the middle scissure of the brain. In a few cases the muzzle will 
be elevated, and the head thrown back, and still the sheep will 
pursue his straightforward course; the hydatid will then be 
found on the cerebellum, or occupying the fourth ventricle. 
Very prevalent .—This is a sadly prevalent and fatal disease in 
some w r et and moorish districts, and in cold and backward 
springs. It is particularly fatal in the greater part of France. 
It is supposed that at least 900,000 sheep annually die there of 
the tournis (so the malady is called in France). We give it 
many strange, yet not altogether unmeaning names, the gig, 
goggles, turnsick, sturdy. 
Strange Opinions of its Cause .—Old writers attributed it to 
various other causes; as, the poisonous effect of certain plants, 
or the consequence of exposure to hoar frost. Some have consi¬ 
dered it to be a species of serous apoplexy; others the result of the 
