3o8 Veterinary Medicine. 



greater number of hosts of different genera, and finds its home in 

 so many different organs of the infested body, that it is especially 

 injurious and often fatal to the animals infested. 



Habitat and Host. Entering as it does by the alimentary canal 

 it most commonly makes its way to the liver to make its home 

 there, but it is found not infrequently in the spleen, abdominal 

 walls, kidneys, brain, lungs, pleura, connective tissue, bones and 

 other structures, of man, ape, ox, sheep, deer, camel, giraffe, 

 horse, pig, elephant, rabbit, turkey and many other animals. 

 Most herbivora and omnivora appear to be open to its attacks, 

 and almost any organ of the body may be invaded. 



Development. The ova laid by the ripe proglottis, and partic- 

 ularly the minute six-hooked embryo are introduced into the 

 stomach and intestine, and the embryo at once begins to bore 

 through the walls to reach a congenial larval home. They ap- 

 pear to travel first in the blood of the portal vein, and the ma- 

 jority are arrested in the liver, while others continue in the blood 

 stream to reach distant parts and organs. Some doubtless reach 

 the peritoneum direct, and develop in that membrane or on one 

 of the abdominal organs. At first growth is slow and in four 

 weeks they may be represented by .small globular cysts less than 

 I mm. in diameter. The.se are usually directly under the serous 

 membrane (in splanchnic cavities) but they may also be in the 

 interior of a solid organ. In about eight weeks each has attained 

 a diameter of -^-^ inch and shows on its inner surface a layer of 

 nucleated cells, the first trace of the inner or germinal membrane. 

 At about the end of the fifth month it has reached the size of a 

 walnut showing a whitish, translucent, tremulous sac enclosed in 

 a double membrane, the outer layer of which (hydatic membrane) 

 is thick and dense (.2 mm.), and the inner (germinal membrane) 

 thin and delicate (.12 mm.) thicks The contents are saline, 

 neutral, or slightly acid and among other things contain a 

 poisonous alkaloid (leucomain) to which have been attributed the 

 skin eruptions that appear when the cyst has burst into a large 

 serous cavity. Exceptionally the ecchinococcus may be arrested 

 at thisi point and remain a simple sac destitute of head or other 

 definite organ (acephalocyst). 



More commonly after some months interval the internal mem- 

 brane (endocyst) develops papillary elevations on its inner sur- 



