142 ENTOZOA FOUND IN MAN. 



of the cranium, as its bony parietes place an insuper- 

 able obstacle in the way of an examination. 



In those cases in which the natiure of a large-sized 

 tumour has remained undetermined, the diagnosis 

 may be settled by an exploratoiy puncture. A clear, 

 limpid fluid extracted from the tumour, not coagu- 

 lating upon the addition of acids or the application 

 of heat, and leaving crystals of chloride of sodium 

 after the evaporation of a few drops of the fluid 

 placed upon a piece of glass, may generally be 

 referred to hydatids. A turbid liquid, of a sero- 

 purulent character, and which presents an athero- 

 matous appearance when examined by the microscope, 

 may also be considered as derived from hydatid 

 tumours. Under either conditions, echinococci or 

 their hooks are very frequently found in the fluid. 



The exploratory puncture has been regarded by 

 many writers as being dangerous when it passes 

 through a serous cavity ; but if it is made with a 

 capillary trocar, the risk is really very smalL 



When the cyst has been ruptured, the expulsion 

 of hydatid membranes either through the natural 

 passages, or through an adventitious opening, renders 

 the diagnosis perfect ; but a simple ocular inspection 

 is not always sufficient to decide whether the mem- 

 branes which are expelled are those of hydatids. 

 These fragments have a peculiar appearance ; they 

 are, as has already been stated, formed of very fine 

 layers, arranged one upon another, which, when 

 examined by the microscope, exhibit upon their 

 transverse section parallel lines, somewhat similar to 

 the leaves of a book. 



The diagnosis may, at the same time, be confirmed 



