PARASITES OF ANIMALS. 171 



they, becoming encysted, patiently await the day when the 

 destruction and digestion of their host shall make possible their 

 final development into tape-worms. 



One of the tape-worms which infest the intestines of the dog in 

 like manner, while immature, passes its encysted state in the brain 

 of the sheep, thereby causing that troublesome disease, the 

 staggers. 



The matured joints of the tape-worm escaping from the dog 

 with its fecal matter, are scattered upon the ground and the eggs 

 adhering to the wet grass, are swallowed by the sheep, in whose 

 stomach and intestines they are hatched ; the embryos beings are 

 armed with six little hooks with which they actively make their 

 way to the points where they may properly become encysted. To 

 do this they have only to enter a circulating vessel and be carried to 

 the brain along with the curreut of blood, or to such other, place as 

 their instincts determine, when they fix themselves and becom- 

 ing encysted, they await the time when they may pass into the 

 stomach of some suitable animal in which to fulfill their final 

 destiny. 



The pig and man stand in the same relation — the tape-worm in 

 man, in becoming matured, produces millions of eggs, some of 

 which will easily be swallowed by swine, and hatching, will 

 migrate, and becoming encysted, produce "measly" meat. This 

 if swallowed without thorough cooking, may give rise to tape- 

 worms as before. The remedy is thorough cooking or abstinence. 



Many other similar instances might be cited ; the law appearing 

 to be in all, that two hosts are required for the complete evo- 

 lution of the tape-worm — one of these furnishing the home for the 

 cestoid development, the other for the tape-worm proper. More- 

 over one of these hosts is destined to be eaten by the other ; 

 hence we should not expect to find the tape-worm in the intestine 

 of an herbivorous animal, like the sheep and ox. And as a matter 

 of fact these do furnish the encysted worm which give rise to the 

 staggers, by the inflammation and pressure they cause in the 

 brain — but not the tape-worm, since they do not devour other 

 animals in which the encysted forms occur. 



However, it is easy to see that exceptions to this rule 'may occur; 

 thus, the dog may swallow the eggs of the matured worm, which 

 have escaped with his own feces, and thus become infected with 

 the encysted worm, and some of these may be discharged by 

 ulceration into the intestines where they will reach their final and 



