124 ENTOZOA FOUND IN MAN. 



liable to the attacks of vesicular worms, which have 

 not been met with in the synovial cavities, or in the 

 peritoneum, in man, unless they happen to have 

 reached the latter cavity accidentally, owing to the 

 rupture of a cyst situated in one of the abdominal 

 viscera. 



The cavities in which vesicular worms have been 

 observed in a free state in man are the cerebral 

 ventricles, the arachnoid membrane, the chambers of 

 the eye, the pleura, the pericardium, and the tunica 

 vaginalis testis. 



Although this enumeration suffices to show that 

 vesicular worms may live in a free state in most of 

 the natural serous cavities, they are not very often 

 found in these situations, especially in man ; and it 

 is, in fact, in the parenchymatous organs that they 

 most frequently make their habitat ; they are, how- 

 ever, separated from the tissue composing these 

 viscera by an adventitious pouch or cyst, whose 

 structure is analogous to that of a natural serous 

 membrance. 



In whatever part of the body the vesicular worms 

 may be developed, they possess no action upon the 

 viscus in which they are contained except indirectly, 

 through the medium of the membrane which encloses 

 them, and this action presents no difference, whether 

 they are contained within a natural or an adventitious 

 cavity, as the effects produced by these entozoa are 

 only those which result from compression. 



The lesions which are produced by the existence 

 of hydatids in man will be first discussed ; and, 

 subsequently, those which are produced by the 

 presence of cysticerci. 



