GLANDS. 479 



them to have great affinity to embryonic cells ; for the acid 

 dissolves the cell-membrane completely away, and leaves 

 the nucleus of the cell (the dotted corpuscle) unaffected by its 

 action." 



Lining each follicle, Mr. Simon has detected a delicate and 

 homogeneous structure, which he has termed the " limitary 

 membrane : " this structure is identical with the basement 

 membrane of Bowman, and is probably common to all glands, 

 especially the follicular ones. 



Mr. Simon has likewise described a lobular arrangement 

 of the follicles. The structure of the gland resolves itself, he 

 says, " into masses ranged round an axis. Each mass con- 

 stitutes a sort of cone of glandular substance, its apex pointing 

 to the axis or mesial line of the gland ; its base directed to 

 the surface, where it presents innumerable vesicles ; while 

 its intermediate part contains those successive branchings of 

 the follicle which terminate superficially in the vesicular 

 form." 



THYROID GLAND. 



The anatomy of this gland is best studied in a specimen 

 which has undergone a slight enlargement of its several parts : 

 a portion of such a gland, when viewed with the inch object- 

 glass, bears so close are semblance to a mass of fat, that, except 

 by a practised microscopist, it would be impossible to dis- 

 tinguish it therefrom with such a low power ; even when 

 viewed with the half-inch, the illusion would scarcely be dis- 

 pelled, and it is only on the application of the quarter-inch 

 glass, that misgivings would begin to be entertained in re- 

 ference to its identity with fat. 



The resemblance borne by a portion of thyroid gland thus 

 slightly enlarged by disease to a mass of fat, arises from the 

 form of the vesicles or closed cells of which the gland is com- 

 posed, and from the manner in which they reflect the light, 

 the centre of each vesicle being clear and bright, and the cir- 

 cumference dark and almost black ; here, however, the re- 



QQ 3 



