PARASITES OP ANIMALS. 77 



pork, is fully explained. Since these facts have been ascer- 

 tained, search has been made for " measles" in beef from 

 animals not experimented upon, and they have been found in 

 several instances. 



When such beef is swallowed by man, without cooking, the 

 young tape-worms are liberated from their capsules or cysts 

 by the process of digestion ; the head becomes protruded, and, 

 passing into the intestine, it fastens upon the lining mem- 

 brane by its suckers. There it rapidly grows larger, new 

 joints are developed, and the body grows longer and longer, 

 the form of the joints changing as they grow, until those that 

 are most mature become square, and finally oblong, as shown 

 in Figure 57, which represents a beef tape-worm, of natural 

 size, in several sections, the intermediate joints being omitted. 

 When full grown, which requires three or four months, one of 

 these tape-worms may contain over 800 joints, of which 860 

 to 400 of the last ones will be sexually mature, each one con- 

 taining 5000 or more eggs. This species is much larger than 

 the pork tape-worm (T. solium}, as well as longer, its length 

 being sometimes twenty feet, and its greatest breadth half an 

 inch, while the joints are thicker and stouter, or have a plump 

 look, instead of being thin and flat, as in the other. The 

 head, as already intimated, is quite different in the two species 

 that of the beef-worm being larger and flat, or even concave, 

 at the end, with four large suckers on the sides, as shown, 

 greatly magnified, in Figure 58. The joints themselves are 

 very different internally, the egg-masses or uteri being very 

 numerous, and crowded together in a more parallel manner 

 (Figure 59) in this than in the pork tape-worm, in which 

 they are fewer and more aborescently branched. The mature 

 joints, filled with eggs, are cast off, as in other tape-worms, 

 and leaving the intestine, have an independent existence for 

 a few days, when they burst by the enlargement of the embryos 

 in the eggs. The eggs are thus scattered about in manure, in 

 water, in the drainage of cess-pools and sewers, by the winds, 

 and by insects. It is not strange, therefore, that cattle should 

 occasionally swallow such eggs with their food and drink, 

 especially if we reflect that one man, harboring only one of 



