316 ANIMAL PARASITES. 



3. The mode in which the human subject is infected with 

 Trichina spiralis, from the preceding indications, must be analo- 

 gous to what we have already stated with regard to the infection 

 of man with Cysticercus cellulosa. Here, also, we may suppose the 

 following things to be possible. The most probable supposition is, 

 that the female of the worm appertaining hereto (Trichocephafus) 

 scatters her young in the intestine of her human host ; and 

 these, after escaping from the egg-shells, bore through the walls 

 of the intestine, and further en through the body, especially 

 towards the primitive fasciculi of the muscles, where they encyst 

 themselves, like the Cysticerci, being incapable of becoming 

 developed immediately to mature worms {Trichocephalus) within 

 the human intestine. In this case it would certainly be neces- 

 sary that the embryo, which is to become a Trichina, should 

 either possess a boring apparatus, or be capable of bringing its 

 oral organs to a point in such a manner as to adapt it 

 for boring. However, it is still an undecided question whether, 

 with the brood of nematode worms, as with that of the 

 Cestoidea, it is necessary for further development, that 

 the eggs, with their brood, must first have passed the stomach of 

 a host. 



Man might consequently swallow the brood of the species of 

 worm belonging to Trichina (Trichocephalus) with drink; or, if 

 the mature animal dwells in the human intestine, it might be 

 carried back to the stomach by tendency to vomit, escape here, 

 bore through the alimentary canal, and establish itself in the 

 muscles of the body. From the great number of Trichinae 

 which occur, their introduction with drink is perhaps the least 

 probable. 



Whether the brood swims freely in the water, and bores its 

 way into the human body from without, is a question which 

 may certainly be proposed, but which can hardly be answered in 

 the affirmative. 



In this way it would almost appear as if the immigration of at 

 least some of the roundworms inhabiting thehuman intestines takes 

 place in the same manner as that of Taenia solium by the use of flesh 

 which is impregnated with the immature germs of the round- 

 worms in question, whilst the immigration of those which occur 

 in the muscles is sometimes direct and active from the outside 

 (Filaria medinensis), probably connected with the season of the 

 year, and sometimes passing from the exterior {Trichina spiralis), 



