THE DISEASES OF CATTLE. 287 



direction by means of the succeeding pairs of hooks, which it 

 uses like a person who, in attempting to get out of a bow- 

 window, thrusts himself forward by his elbows. In this way 

 the minute embryo penetrates the body it inhabits, and only in- 

 creases its eflforts on reaching the place its instinct recognizes 

 as suitable for its abode, prior to the next series of changes 

 it has to undergo. Streaks of re-active inflammation and 

 exudation generally indicate the minute channel by which 

 the embryo thus traverses the wall of the digestive canal, in 

 its course to the liver or other organs. The migration of a 

 taenia is probably a passive process. Various facts suggest 

 it to be so — * a true locomotion, effected under the impulse 

 of an instinct, and by means of certain special organs. The 

 germs of parasites are evidently carried through the system 

 in the stream of circulating blood, and they do not always 

 travel themselves through the interstices of tissues.' 



" Sturdy was long considered as dependent on a simple ac- 

 cumulation of water on the brain, generally affecting one side. 

 Loecke had observed, in 1780, that the water-bladders on the 

 brain of giddy sheep were animals ; and Fabricus (Harvey's 

 master) was the first to assert the same respecting the cys- 

 ticercus of the pig. Albildguard, the founder of the Copen- 

 hagen Veterinary School, observed that a tape- worm (the 

 bothriocephalus latus) which existed in the abdominal cavity 

 of the stickle-back, and in the intestinal canal of certain water 

 birds, never had eggs in the former but only in the latter situa- 

 tion ; and that from the first-mentioned creature it passed into 

 the second, he ascertained by direct experiments with ducks, 

 which he fed on banstick4es. Goetze, in 1782, had perceived 

 the great resemblance between the head of the hydatid of the 

 liver of mice and rats, the cysticercus fasciolaris, and of the 

 tape-worm of the cat, taenia crassicollis. The cercariae was first 

 studied by Miiller, and lastly by Bejanus, in 1818, who recog- 

 nized them as parasitic, in certain snails, inclosed in bags. M. 

 Wagner and Von Siebold and Steenstrup fancied they had 

 discovered the change cercariae underwent to become true 

 fluke-worms. Ehrenbreg, in 1852, disputed Steenstrup's ac- 



