XXVII.] 



THYROID GLAND. 



301 



stain them either in hasmatoxylin or picro-carmine. Stain in bulk 

 and cut in paraffin. 



(.) (L) Observe the pleura sending well-marked septa into the 

 lung, thus denning the lobules, which are polygonal, about i mm. 

 in diameter, and separated from each other by connective tissue. 



(/;.) In each lobule sections of bronchi, which can be seen 

 occasionally to terminate in several vesicles, thus presenting a very 

 gland-like arrangement (fig. 291). Many of the alveoli are cut 

 across, and appear like sections of tubes lined by columnar epithe- 

 lium. There is much embryonic connective tissue between the 

 alveoli. 



(H) Select an alveolus, and note that it is lined by a layer of 

 low, columnar, granular epithelium, while individual alveoli are 

 separated from each other by much embryonic connective tissue, 

 with numerous cells, and as yet few or no elastic fibres. 



THE THYROID GLAND. 



Methods. (i.) Harden pieces of the human thyroid, or the 

 complete thyroid of a cat or dog, in M tiller's fluid (3 weeks) and 

 then in alcohol. Sections are stained with hsematoxylin and 

 mounted in balsam. 



Or stain in bulk and ^ - . -V^ w >' 



cut in paraffin. 



(ii.) Fix in Flem- 

 ming's fluid (1-3 

 hours), and stain 

 wash thoroughly, 

 alcohol with Ehr- 

 lich-Biondi fluid, or 

 stain with Heiden- 

 hain's logwood. 



11. T.S. Thyroid 

 Gland. (.) (L) 

 Composed of small 

 polygonal lobules 

 united to each other 

 by loose connective 

 tissue. In each lob- 

 ule a iarije number 



FIG. 292. T.S. Thyroid Gland, a. Closed vesicle. 



of completely closed acini held together by loose connective tissue. 

 (/;.) (H) The spherical acini (tig. 292), bounded by a basement 

 membrane, are lined by a single layer of low cubical epithelium, and 

 contain a homogeneous fluid. This fluid, however, is often of a 



