THE ANIMAL PARASITES OF MAN 503 



flukes need not necessarily be with measly meat ; it may be brought about by 

 secondary conditions. It is impossible to enumerate all the accidental ways by 

 which the flukes may be transmitted to food, especially in butcher shops and 

 restaurants in which proper cleanliness is lacking. The transmission of the 

 bothriocephalus latus occurs in a manner similar to that of the eysticerci, the 

 booklets of which are shown to retain great vitality in smoked or frozen pike. 



The role assumed by insects, especially the common house-fly, in the dis- 

 semination of parasites is very interesting. Grassi has shown that the ova 

 of the tenia solium, oxyuris vermicularis, and trichocephalus dispar, pass 

 through the intestine of the fly without change. But Stiles reports that the 

 ova of ascarides undergo further development in the intestinal canal of the fly. 

 Owing to the very general prevalence of flies and their habit of settling upon 

 various food-stuffs, on which they defecate, there can be no doubt that these 

 insects contribute materially to the distribution of the ova of the helminthes. 

 It is certain that vegetables of various kinds and sources, if not thoroughly 

 washed, or if eaten raw, may become the carriers, the same as meat if it has 

 but come in contact with the ova of helminthes. 



We know, from the interesting observations of Lutz, how the ascarides de- 

 velop. The rural population especially, and, above all, the children by play- 

 ing upon infected soil, acquire the embryos of. the ascaris lumbricoides from 

 the soil, whereas the parasites are far less frequent among city-bred people, 

 even among the children. The affection is often transmitted by food con- 

 taminated with infected earth, often by means of the drinking-water into 

 which germs capable of development have lodged. 



The role of drinking-water in the distribution of the entoparasites is un- 

 doubtedly of great importance. I do not refer only to the transmission of 

 occasional parasites, but, above all, to the protozoa, the ova of ascaris and of 

 trichocephalus, especially the immature forms of the trematodes, which reach 

 the human intestinal canal by polluted drinking-water. Water has an influ- 

 ence also in the development and distribution of the ankylostoma duodenal e, 

 as we shall see later. Since the investigations of Loos, it can no longer be 

 doubted that the last-named parasite is- able to force its way into the human 

 organism through the uninjured shin. A number of authors believe this true 

 also of the filiaria medinensis (guinea worm). So manifold are the ways in 

 which the young forms of the parasites, or the parasites themselves, migrate 

 into man that we cannot enter upon them here. 



When we endeavor to ascertain whence the former originate, we note that 

 the majority of parasites are derived from animals, especially from our domes- 

 tic animals, dogs, cats, pigs, and cattle. I refer only to the group of the 

 cestodes, to the trichina, and to numerous epizoa. The more intimate the 

 relations between animal and man, the greater the danger of transmission. 

 Furthermore, man himself is often not only the carrier, but the disseminator 

 of the parasites. Not only does he infect his surroundings with the young, 

 but occasionally he infects himself, as shall be demonstrated later in the dis- 

 cussion of oxyuris vermicularis. 



In regard to the symptomatology, there is perhaps no realm of pathology 

 in which so many contradictory opinions have been expressed as have been 



