DOMESTIC ANIMALS AS SOURCES OF PARASITES. 159 



bladder- worms, as statistical results clearly prove. Thus, according to 

 official reports, there are above 30,000 swine eaten yearly in Leipsic, 

 out of which, according to the results of the Brunswick investigations 

 (which furnish as yet the most favourable fraction one trichinous 

 pig in 5000), there ought to be at least six infested with Trichina. 

 If the parasites were not rendered harmless by cooking, we ought 

 obviously to expect six epidemics of Trichina yearly, while in reality, 

 apart from a few isolated cases, there have been only two observed 

 since 1860 a severe one in the winter of 1877, and another less 

 serious. In Sweden, where in many districts 1 per cent, of the swine 

 are trichinous, the disease is only known as a sporadic malady, and 

 as such only rarely. 1 



We have spoken mainly of the pig and the ox, since these animals 

 furnish the largest proportion of the food used by civilised peoples, 

 and, so far as we know, are the most common sources of parasites. 

 But we are also aware that other kinds of flesh may also infect us 

 with parasites. Thus the goat harbours the cystic stage of Tcenia 

 saginata, though not so frequently as the ox; the sheep and deer 

 sometimes contain the bladder- worms of Tcenia solium. Further, we 

 may find Trichina in the flesh of martens, foxes, rats, and hamsters 

 which are here and there used as food. The assertion of Herbst, that 

 pigeons and other birds were also infested with encapsuled Trichina, 

 is based on an error, for we are not yet acquainted with any bird 

 capable of infecting man with worms. It is otherwise with fishes, for 

 we have obtained convincing proofs through the observations and ex- 

 periments of Braun, 2 in Dorpat, that the pike (although it remains 

 questionable whether this is the only fish that does so) yields young 

 stages of Bothriocephalus latus to human beings. It is to be assumed 

 that Bothriocephalus cordatus of Greenland is also derived from the 

 flesh of some marine fish which harbours its young stage. It is found 

 not only in man but in dogs, which are fed by the Esquimaux, for the 

 most part, on raw or dried fish. At any rate, it must be some in- 

 habitant of the water which harbours the young stage of the human 

 Bothriocephalus, as we infer with every certainty from the cili- 

 ated coating, by means of which the embryos are able to swim 

 about. 3 



The introduction of the germs of Helminths can also easily take 

 place through small terrestrial or aquatic invertebrates. Chance 



1 See Vol. II. 



2 Braun, " Zur Entwicklungsgeschichte des breiten Bandwurmes : *' Wiir/burg, 1883. 

 8 The assertion of Knoch ( Virchow's Arckivf. pathol. Anat, Bd. xxiv., p. 243 et seq., 1862) 



that Bothriocephalus is developed without an intermediate host, was suspicious in the highest 

 degree, even before Braun adduced arguments against it. (See under " Bothriocephalidae," 



