210 PARASITES OF THE DOMESTIC ANIMALS 



an especial value. Cold packs upon the head or continuous irrigation, 

 accompanied by purgatives, have been recommended for the acute 

 stage, but such treatment can be no more than palliative, and is scarcely 

 practical unless under exceptional conditions. 



In general, it is better, from considerations of economy, to slaughter 

 animals upon the first evidence of gid. 



Echinococcosis 



Hydatid Disease. 



Hydatid disease is caused by the presence of Echinococcus granulosus 

 (E. polymorphus, E. multilocularis, etc.) or so-called hydatid, the cystic 

 stage of the tapeworm of the dog, — Echinococcus granulosus {Tcenia 

 echinococcus), elsewhere referred to under the cestodes of that animal 

 (p. 181). It occurs in man and all of the domestic mammals, the hy- 

 datids usually located in the organs of the abdominal or thoracic cavity, 

 most often the liver, though not infrequently the lungs, spleen, serous 

 membranes, and other organs, several of which may be affected in the 

 same animal. The disease is as cosmopoKtan as dogs and their par- 

 asites, therefore it is of world-wide prevalence. 



The Echinococcus (Fig. 117). — While the echinococcus is the largest 

 of the tapeworm cysts, the dog tapeworm, of which it is the larval form, 

 is but 5 mm. (3/16 of an inch), or thereabouts, in length, and consists 

 of a head and three segments. When uninfluenced by pressure, the 

 echinococcus cyst is more or less spherical in shape and presents a com- 

 plex structure, the parts of which may be set forth for study as follows: 



1. An external cuticular membrane (hydatic membrane). 



2. An internal germinal membrane. 



3. The fluid which distends the vesicle. 



4. The proligerous vesicles, which contain the larval tapeworm heads. 



5. The daughter vesicles. 



Surroundiag the whole is a capsule formed from the connective 

 tissue of the organ in which the structure is lodged. 



1. The cuticular membrane limits the echinococcus externally. It 

 is whitish in color, concentrically laminated in structure, and in large 

 vesicles may attain a thickness of 1 mm. 



2. The germinal membrane is much thinner than the cuticular, 

 usually not exceeding 20-25 microns in thicknes^. On its internal sur- 

 face there appear groups of small papillte, representing the beginning 

 development of the proligerous vesicles. 



3. The hydatic fluid is colorless or yellowish and in reaction is neutral 

 or slightly acid. It may contain a number of substances, mostly de- 

 rived by endosmosis from the blood and lymph of the organ invaded. 



4. The proligerous vesicles appear on the internal surface of the 



