THE TAPEWORM LARVAE 197 



are affected, which, in addition to the exposure of human beings to 

 tapeworm infection, is a matter involving considerable economic loss 

 in the condemnation of beef otherwise of perfectly good food value. 



When it is considered that the gravid segments of the beef tapeworm 

 each contain in the neighborhood of ten thousand eggs, and that eight 

 to ten of these segments are usually passed by the himian host each day, 

 it is quite evident that, under certain not unusual conditions, the in- 

 fected person could be responsible for the presence of the cysticerci in a 

 large number of cattle. The chances for such transmission will be in 

 relation to the location and habits of the carrier of the tapeworm. If 

 it is his custom to defecate about stables or barnyards, the chance that 

 some of the many thousands of voided embryos will reach their bovine 

 hosts is obviously much increased. Where himaan excrement is used 

 for soiling without its first having been made non-infective by special 

 treatment, cysticercus infection among cattle and hogs is especially 

 frequent. 



Measles is more often foimd in yoimg than in aged animals. This is 

 probably explained by the fact that beef animals are usually slaughtered 

 young and are more susceptible to infection during the first two years of 

 their life when the tissues offer less resistance to the migration of the 

 embryos. In aged animals the cysts are likely to be in a state of ad- 

 vanced degeneration or entirely absorbed. 



Location and Appearance. — The cysticerci may be found in any 

 organ, but are more especially to be looked for in the interfascicular 

 connective tissue of striated muscle (Fig. 108). Of the muscles invaded, 

 the first to be mentioned in order of frequency are those of mastication, 

 chiefly the pterygoids and masseters; following these are the heart — 

 which is probably as frequently infested as the masticatory muscles — 

 the muscles of the neck, intercostals, and muscular portion of the 

 diaphragm. In any case it is unusual to find the cysts numerous through- 

 out the muscle, though cases occur of general invasion involving most 

 of the organs of the body. 



The size and appearance of the cysts vary in relation to their age and 

 stage of development. Experimental infections have shown that iff 

 seventeen to twenty-five days they measure 2-^ mm. (3/32-3/16 of an 

 inch) in length and 1.5-3 mm. (1/16-1/8 of an inch) in breadth. They 

 are grayish white in color, the outer connective tissue envelope inclosing 

 a fluid which surrounds the clear vesicle or bladder worm. This is 

 0.5-1.5 mm. (1/32-1/16 of an inch) in diameter, and has at one point a 

 yellowish white spot indicating the location of the invaginated scolex 

 which will evaginate on pressure upon the vesicle. 



Experiments by Hertwig have demonstrated that the cysts become 

 fully developed in eighteen weeks after the occurrence of infestation. 

 At this time he found the entire dimensions of the larger cysts to be 



