OF HYDATIDS. 267 



"t have several preparations, which afford a 

 striking illustration of the manner in which bone 

 is formed on the coats and sac of hydatids. The 

 ossification begins from a few central points on the 

 coats of the hydatid, and by subsequent depositions, 

 the pieces of bone gradually become larger and 

 larger, so that at length a considerable mass of 

 bone is formed.'^ 



*' 0^ the manner in which the cysts of hydatids are 

 formed. 



"The sac, containing the hydatid, seems to be 

 formed in consequence of the irritation of the hyda- 

 tid. In the same manner, where a large quantity 

 of purulent matter has been contained within the 

 viscera, we generally observe a sac, provided with 

 arteries, veins, nerves, and lymphatics, as is ob- 

 vious from the very varied contents of these differ- 

 ent sacs, and the spontaneous removal or absorp- 

 tion of their contents. There are also similar in- 

 stances in the vegetable kingdom, as in the pro- 

 duction of galls from the oak, &c.'' 



" Of the effects of hydatids, on the organs which 

 contain them. 



*^ Hydatids, which attain a considerable bulk, 

 not only mechanically affect the organ within which 

 they are lodged by their pressure, but, by the ir- 

 ritation which pressure gives, produce still fur- 

 ther changes upon it. On acccount of the particu- 



