156 THE EFFECTS OF PARASITES ON THEIR HOSTS. 



which only exceptionally occur. Further, our deeper insight into 

 the life and developmental history of Oxyuris has rendered Ktichen- 

 meister's supposition, which was never directly proved, somewhat 

 obsolete and gratuitous. 



Although the number of the parasites which we thus derive by 

 external contact from man and beast is by no means a small one, yet 

 it is very considerably exceeded by that contingent which we acquire 

 along with our food and drink. The ox, whose flesh we eat, harbours, 

 as we know, a whole host of young worms (Figs. 91 and 92), which 

 only become mature in the human intestine. From the pig we 

 derive Trichina and Tcenia solium, from the ox Tosnia saginata, just 

 as the cat gets its tape-worm {Tcenia crassicoUis) from the mouse, and 

 the mouse its Spiroptera from the meal-worm {Tenebrio molitor). In 

 regard, then, to the helminthological relations of animals, this is the 

 first and most general law, as we have already remarked (p. 80), that 

 the carnivorous animal derives a great part of its Entozoa from its food. 

 But besides the animals actually eaten as food, those also contribute 

 their Entozoa which are accidentally swallowed or carried in some 

 way into the alimentary canal. This mode of introduction (p. 80) 

 obtains among the Herbivora; and of course it is not man only, 

 with his almost equally vegetarian and carnivorous diet, that is 

 subject to these parasites, but even the Carnivora, which avoid vege- 

 table food, are not safe from their accidental importation. 



We shall discuss in the first place the transmission of parasites hj 

 the use of flesh as food. 



When flesh is eaten raw, as is the custom in Abyssinia and else- 

 where, the possibility of transference requires no special proof. The 

 worms thus swallowed develop as surely and constantly as in animals 

 under experiment, provided only that they find in their new host 

 the conditions essential for their further development, and that they 

 are not injured by the mechanical processes of eating. It is thus 

 sufficiently evident why Taenia saginata is found in young and old 

 among the Abyssinians who eat raw beef, and why Europeans are 

 also rapidly infested when they begin to live cb V Abyssinienne. 



It is obviously otherwise among civilised peoples, where it is 

 customary to cook the flesh used as food. The danger of infection 

 with the young worms is by this means to some extent lessened, 

 though the protection thereby afforded is only a limited one. 



We may first of all note that, in spite of the general prevalence of 

 the custom of cooking food, there are yet bye-ways open for the intro- 

 duction of parasites. Raw meat is prescribed by the physician in many 

 diseases as a specially nutritious food. During the preparation of 

 certain kinds of food (especially sausages and meat-balls) the raw 



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