OUE DOMESTICATED ANIMALS. 121 



given in my Cantor Lectures {Journal of the Society of 

 Arts, 1871). 



In this place I deem it unnecessary to recapitulate the 

 facts of fleshworm parasitism at any great length. In 

 the hog, as our experiments at the Koyal Veterinary 

 College freely demonstrated, these worms do not appear 

 to be capable of occasioning inconvenience to the bearer ; 

 at least, the pig, in which I reckoned we reared some 

 sixteen millions of encysted muscle-trichinae, never 

 showed the slightest indications of suffering. In other 

 animals, however, as well as in man, this immunity from 

 symptoms of irritation is seldom preserved under like 

 circumstances. 



Stating the matter in the briefest possible terms, we 

 may say that the Trichina requires about three weeks to 

 run its course of development, commencing and ending 

 with the encysted condition in which it was originally 

 discovered. This is the state here represented from one 

 of Professor Pagenstecher's admirable illustrations (Fig. 

 28). The ingestion of muscle-trichinae by any suitable 

 bearer ensures the completion of the adult growth of the 

 worm in the intestine of the host in two days. In six 

 days more the embryos will commence to leave the body 

 of the female worm, and immediately set about penetra- 

 ting the walls of the intestine, in order to arrive at their 

 destination in the most direct manner available. Having 

 at length wandered into and secured a resting-place 

 within those voluntary muscles which are well supplied 

 with connective tissue, they will (after the further expira- 

 tion of fourteen days from the time they commenced 

 their migration) eventually have acquired the well-known 

 form and size of the perfected muscle-trichina. 



The so-called lemon-shaped, or oval cysts, in which the 



