298 DR. T. S. COBBOLD ON HUMAN ENTOZOA, [NoV. 25, 



marked differences existing between the males of Trichocephalus 

 affinis and T. dispar. The presence of the last-named species in the 

 human body is fortunately attended with very little inconvenience ; 

 but its development and mode of gaining access to the host has 

 nevertheless been recently made the subject of diligent inquiry. 

 Leuckart's, and especially also Virchow's, researches have entirely 

 disproved Kiichenmeister's notion that Trichince are the young of 

 Trichocephalus ; and the experiments of Davaine render it probable 

 that the young get into the human body in a manner very similar to 

 those of Ascaris lumbricoides. The latter authority finds that the 

 eggs undergo no development whilst yet lodged within the host's 

 intestine, and they are expelled per anum in the immature condition 

 in which they make their escape from the body of the parent worm. 

 It further appears that, after their expulsion, a period of six months 

 must elapse before the embryonic formation commences — an inter- 

 esting circumstance, and one which satisfactorily explains why it 

 was that my own feeding-experiments (on a chicken and rabbit) with 

 the fresh eggs of Trichocephalus affinis gave only negative results. 

 According to Davaine, the fully developed embryo measures y-l-^rd 

 of an inch in length, and to a certain extent resembles the parent, 

 tapering gradually from behind forwards. 



13. Trichina spiralis, Owen. 



T. spiralis, Owen, Wood, Farre, Henle, DifFenbach, Fricke and 

 Oppenheim, Paget, Knox, Harrison, Hodgkin, Leblond, Siebold, 

 Kobelt, Nordmann, Valentin, Bischoff, Dujardin, Svitzer, Luschka, 

 Kiichenmeister, Gairdner, Sanders and Kirk, Oobbold, Herbst, Zen- 

 ker, Virchow, Leuckart, Weinland, &c. 



The experimental researches of Herbst, Leuckart, and more espe- 

 cially those of Virchow, afford us an almost complete knowledge of 

 the development and economy of this minute parasite, the facts of 

 which may be briefly summed up as follows: — (1.) Trichince are 

 introduced into the human body by the ingestion of trichinous pork. 

 This diseased meat, if imperfectly cooked or indifferently prepared in 

 the form of sausages or hams, is capable of giving rise to severe fe- 

 brile symptoms in those who partake of it ; and in the case of a 

 woman under the care of Prof. Zenker, of Dresden, it was the sole 

 cause of death. There is reason to believe others have likewise 

 perished from a similar cause. In hams long prepared and well 

 smoked the Trichince are found dead ; they resist death in decom- 

 posing flesh, also during a prolonged immersion in water ; in the en- 

 cysted condition they are unaffected by tolerably strong acid solu- 

 tions. (2.) Trichina spiralis forms the type of a distinct genus of 

 nematodes ; it has no genetic relation whatever to Trichocephalus 

 dispar ; it reproduces viviparously like Filaria draeunculus. (3.) Non- 

 encysted Trichince may exist in the flesh of animals without being 

 visible to the naked eye ; whilst encysted TrichincR, where cretifica- 

 tion has not commenced, are difficult of detection without the aid of 

 a pocket lens. The latter observation is based on appearances which 



