520 MR. youatt’s veterinary lectures. 
begin to be inattentive to surrounding objects, and move among 
them as if they were unconscious of their existence. The habit 
of turning round increases; they will continue to form these 
concentric circles for hours together without stopping, or until 
they fall, and they will rise again only to commence the same 
round : at length they die emaciated or exhausted ; or death is 
somewhat hastened by their being unable to extricate themselves 
from the brook or the ditch. 
Proceeding from an Hydatid .—On examining them after 
death, we find an hydatid, a true hydatid, or many of them, be¬ 
tween the pia mater and the brain, and sometimes embedded in 
the cerebral substance. The existence of these hydatids has 
been doubted in the human brain. After enumerating various 
names on the one side and the other of the question, Dr. Cop¬ 
land, in the article on the Brain, in his excellent “ Dictionary 
of Practical Medicine/’ says, that ‘ whether these bodies were 
entozoa, or mere hygromalous tumours or cysts, rests upon the 
pathological reputation of the physicians.’ 
Description of the Hydatid .—There is, however, no doubt 
about the matter here : they are hydatids of the cysticercus tenui - 
collis species (the hydra hydratula of Linnaeus). When they are 
perfectly dissected out, the neck is readily perceived, and also the 
tentacula, or barbs, projecting from the apparent opening or 
mouth, which forms the extremity of it. They vary in size from a 
marble to a pigeon’s egg. A cyst or bladder presents itself, con¬ 
taining a fluid, sometimes a little turbid, and at other times as 
pellucid as water, but with a slight animal taste and smell. There 
is no further organization about them than that they appear to 
have a double or treble investment, the central layer of which 
would seem to be of a muscular character. Sir Everard Home 
says, that, after having submitted them to examination with 
microscopical glasses of a high magnifying power, “ their coats 
resembled paper made upon a wire frame, that is to say, the 
muscular fibres interlaced each other in a way that would satis¬ 
factorily account for their vibratory motion.” The parasite, when 
first extracted and placed in warm water, has an evident vibra¬ 
tory motion ; and if then punctured, the contained fluid will be 
ejected to a considerable distance. The inner membrane is 
clearly marked with rugae, like the stomachs of animals of a dif¬ 
ferent class. 
Mode of Production .—Their mode of production is altogether 
unknown. The ovum or germ, or minute hydatid, may be float¬ 
ing in the atmosphere, or be received with the food, and, like some 
other entozoa, and more particularly like the filaria in the eye of 
3 bloodvessels and 
us, the brain of a 
the horse and the ox, may thread the various 
capillaries until it arrives at its destined nid 
