158 ENTOZOA FOUND IN MAN. 



level of the last dorsal, or of the first lumbar, vertebra, 

 are usually characteristic symptoms of aneurismal 

 tumours in this region. 



Notwithstanding these signs, which are suffi- 

 ciently distinctive in many cases, there are some 

 cases in which the diagnosis presents the greatest 

 difficulties. These difficulties especially arise when 

 the growth of the tumour has been more rapid than 

 is usual, when it is accompanied by pain and febrile 

 symptoms, when some peculiar circumstances, such as 

 external violence, have modified its progress, when by 

 the pressure exercised upon the biliary ducts, the 

 portal vein, or the vena cava, the tumour has pro- 

 duced either jaundice, ascites, or oedema of the lower 

 extremities, or when several cysts give an uneven 

 character to the enlargement in the hypochondrium ; 

 but in all of these cases, if the hydatid-trembhng should 

 be absent, an exploratory puncture with a capillary 

 trocar, when it can be resorted to without danger, 

 would decide whether the afiection proceeded from 

 hydatids, or not. 



Hydatids are much less common in the spleen 

 than in the liver ; and they generally co-exist with a 

 similar disease in the latter organ, or in some other 

 region of the abdomen. They are usually developed 

 in the sub-peritoneal areolar tissue, or in the vicinity 

 of the spleen, and only invade the spleen subse- 

 quently, although they may also originate in the 

 interior of the substance of that organ. They have 

 thinner walls than those which are situated in the 

 liver ; and the surrounding substance often remains 

 healthy. The mode of their development, the size 

 to which they attain, and the changes which they 



