154 THE EFFECTS OF PARASITES OX THEIR HOSTS. 



as not unfrequently happens, issue forth individually and creep about 

 on the body, it may happen that, simply by a wipe of the hand or 

 some other means, they are unconsciously transferred through the 

 mouth to the stomach. 



Encapsuled Trichinae and bladder-worms are not, however, by any 

 means the only Entozoa which man derives from himself. The sup- 

 position of Kuchenmeister, that the Echinococcus also belonged to the 

 number of the " Autochthones " has, however, proved erroneous, for 

 the sufficient reason that the tape-worm, of which it is the immature 

 stage, does not occur in man. 1 On the other hand, we have in 

 Oxyuris vermicularis* a parasite whose transmission very commonly 

 takes place by self-infection. The eggs which under favourable cir- 

 cumstances e.g., a temperature 37'5 C. produce in a few hours a 

 mature embryo, and which are found strewed about in the neigh- 

 bourhood of the infested individual, and often in quantities even on 

 his body, are transferred in various ways, but usually by the hands, 

 to the intestine, and there the embryos escape and rapidly attain 

 sexual maturity. This extreme liability to self-infection, and the 

 continual reproduction of the parasites, are the causes of the persis- 

 tency of 0,r?/ims-disease and of the difficulty of a perfect cure, which 

 is indeed so great that it suggested the possibility of there being eggs 

 which developed directly in the intestine of the host to sexually 

 mature forms. 



Trichocephalus dispar resembles Oxyuris. Davaine believes, 

 however what is not firmly established that the eggs even of 

 Ascaris lumbricoides may, with enclosed embryos, be accidentally 

 introduced into man. The transference is, however, not so direct as 

 in the case of Oxyuris, for between the laying of the eggs and their 

 transference a period of many months usually elapses, during which 

 the eggs have, of course, most diverse fortunes. Nor is it necessary 

 that the eggs be derived from man, for both these worms are found in 

 the pig, though they are then not unfrequently classed as distinct 

 species (Trichocephahis crenatus and Ascaris suillce). 



From these results, we see that we cannot possibly regard our 

 domestic animals as solely responsible for the introduction of the 

 eggs of parasitic worms. We are ourselves partly to blame ; we in- 

 fect our own bodies, and sometimes also those of our fellow-men, just 



1 The opposite opinion rests on a confusion of Tcenia nana, v. Sieb., which is a human 

 parasite, with T. echinococcus, v. Sieb. (7*. nana, van Beneden). The way in which 

 Kuchenmeister uses this confusion (" Parasiten," 2d ed., p. 163, note) as a reproach 

 against me is so strange that I cannot refrain from asking the reader to peruse my harm- 

 less remarks, which have given that author occasion to raise his voice against zoologists 

 (see p. 341 of the first German edition). 



' See Vol. II. 



