138 THE EFFECTS OF PARASITES ON THEIK HOSTS. 



given is sufficient to establish the pathological importance of these 

 phenomena. 



Besides the constant and regular wanderings of the larva, there 

 are similar movements associated with the full-grown animals, but 

 these are, as a rule, only occasional and fortuitous. Among them we 

 class those of Ascaris into the body-cavity, which, of course, pre- 

 suppose perforation of the alimentary canal. 



The possibility of such perforations has been much questioned, 

 both in earlier and more recent times, because the thread-worms are 

 without any kind of boring apparatus. It has also been attempted to 

 explain the numerous cases of this kind mentioned in literature by 

 the supposition that the worms play only a secondary part, since they 

 have been observed, perhaps after the death of the host, to make use 

 in their movements of passages caused by ulcers perforating the in- 

 testine. In proof of the correctness of this hypothesis the character of 

 the perforation has been cited, which seems to be the result rather of 

 a gradual erosion than of a mechanical force. 



Although it is difficult to decide the question with certainty, I 

 think that the denial of the presence of these perforations is quite 

 unfounded. ^ That a boring apparatus is by no means necessary for 

 the perforation of tissues and organs has been decided by modern 

 investigations, and is indeed sufficiently proved by the instances which 

 we have collected of wandering Cysticerci. When we consider the 

 size of these thread-worms, it is, however, evident that they cannot 

 perforate the walls of the intestine with the same ease as the embryos 

 of Trichina. If the boring of the latter be described as an " acute " 

 process, that of Ascaris might be termed " chronic," since it is 

 accomplished by means of a continuous pressure of the head against 

 the wall, a process perhaps resulting not directly in a perforation, but, 

 in the first place, only in certain structural changes in the tissue, 

 which then in turn make the perforation possible. 



In some cases the perforation is not confined to the wall of the 

 intestine. At the umbilicus, and in the inguinal regions, where the 

 abdominal wall yields more easily to pressure, not only the intestine 

 but also the body-wall is perforated. In consequence of the pressure 

 exerted by the parasite, the so-called " worm -abscesses " arise, and 

 inflammation of the connective tissue, which is eventually followed by 

 ulceration, exactly as in the case of the perforations due to Filaria 

 Medinensis. 



Sagittce indiscriminately in all directions. " The poor Sagittce," he says, " of course 

 suffer terribly when the invaders begin their wanderings, and generally die in a tetanic 

 condition, with the hoojcs stretched out stiffly from the head, and the body bent rigidly 

 backwards." 



> See Vol. II. 



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