194 ENTOZOA FOUND IN MAN. 



lined by a delicate layer of areolar tissue, which 

 may be regarded as a tnie cyst ; in some few 

 cases, however, the hydatids were probably developed 

 in a free condition, either in the cavity of the 

 arachnoid, or in that of the ventricles. The hydatids 

 which are developed in the brain-substance itself, 

 appear to be deficient of an envelope of areolar tissue, 

 and to be in immediate relation with the cerebral 

 substance. Those which have their primitive seat 

 in the pia- mater, or in the choroid plexuses, are 

 always contained within a more or less complete cyst. 

 The cyst is very dehcate, possesses only a shght 

 degree of firmness, and is thicker at its free portion 

 than where it is in contact with the cerebral tissue. 



The hydatids, as their development continues, 

 compress the neighbouring parts of the brain, which 

 becomes atrophied, and is sometimes reduced, in the 

 vicinity of the hydatid tumour, to the state of a thin 

 membrane. The nerves, which are in relation with 

 the cyst, in any part of their course, are similarly 

 atrophied ; and, in some instances, the bony parietes 

 of the cranium have been known to suffer from the 

 effects of the enlargement of the hydatid tumour, 

 and to undergo local dilatation, together with atrophy 

 and absorption, in consequence of the continuous and 

 increasing pressure of the tumour. 



Under these latter circumstances, the hydatids 

 may possibly find a means of exit, and the cure of a 

 disease, which might be generally expected to prove 

 mortal, might thus be obtained. An instance of this, 

 referred to by Dr. Davaine, occurred in the hospital 

 at Bordeaux. In such cases, it would be advisable 

 to accelerate the discharge of the hydatid fluid and 



