OCCURRENCE OF THE ADULT TAPE- WORM. 529 



Occurrence and Medical Significance. 

 1. The Adult Tape-Worm. 



As is well known, Tcenia solium is one of the intestinal worms 

 which are found exclusively in man. Von Siebold certainly asserts 

 that he reared tape -worms from the Cystwercus celluloses of the 

 dog, 1 but as he (with Pallas and other older helminthologists) 

 regarded the human tape-worm as identical with the cystic tape- 

 worms of the dog, his results are of course no longer valid. 2 Other 

 investigators, who knew how to distinguish Tcenia solium from the 

 large-hooked tape-worms of the dog, have never succeeded in rearing 

 the bladder-worm of the pig in the intestine of the dog, although such 

 investigators as Haubner, Kiichenmeister, Heller, and myself made 

 experiments on a considerable number of these animals. Just as little 

 success has attended experiments with other mammals, such as pigs 

 and martens (Leuckart), cats, rabbits, guinea-pigs, and apes (Heller). 



Of course, even in man, every bladder-worm does not grow into a 

 tape-worm, nor even every one of those that enters the stomach unin- 

 jured that is to say, with uninjured head. Ktichenmeister estimates 

 the loss in the above-mentioned cases at about 50 per cent., but this 

 estimate has only an uncertain value, since the result must vary much 

 in different cases, both with the more or less thorough mastication and 

 with the nature of the gastric juice. 



The hypothesis of a special predisposition to the tape-worm, which 

 was formerly held on the ground of certain statistical facts, is now 

 abandoned. In every case the occurrence of Tcenia solium depends 

 upon a further development of the Cysticercus cellulosce. Whenever 

 the latter gets into the human intestine in a condition capable of 

 development, there is not only the possibility, but the probability, of 

 this further development, and this is quite independent* of the age or 

 sex of the individual who is infected. The frequency of the worm 

 is always determined by the opportunities given for this reception, 

 and will increase, of course, in proportion as it is favoured and facili- 

 tated by the habits and mode of life. 



As might be supposed from such a state of affairs, Tcenia solium 

 always occurs where the pig is reared and eaten as a domestic animal, 

 and is most frequent where (ceteris paribus) the breeding of pigs is 

 most common. So that Tcenia solium is probably, like T. saginata, 

 cosmopolitan. It is, however, doubtful whether it is so universally 



1 " Band- und Blasenwurmer," p. 87. 



2 This explains the great dissimilarity, in v. Siebold's case, between the administered 

 bladder-worms and the tape-worms which he afterwards found, a fact which even at 

 that time gave rise to the conviction that the dog was but little adapted for rearing 

 the bladder- worms of the pig. 



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