THE THYEOID GLAND 559 



broken into minute spherules. In general, the ratio of colloid content 

 within the follicle, roughly stated, is in proportion to the age of the in- 

 dividual. The follicles at the periphery of the lohes of the gland are 

 less fully distended than those in the interior. 



Embedded in the colloid mass within the follicle, even in the appar- 

 ently normal thyroid, red blood corpuscles and desquamated follicular 

 epithelium are frequently found, but never in large quantity. Leuko- 

 cytes are of less frequent occurrence and are more rarely found in the 

 human thyroid than in that of the lower mammals. 



The FOLLICULAR EPITHELIUM is typically cuboidal in shape; in 

 young individuals it is somewhat taller than broad. In those follicles 

 which are distended with colloid secretion the epithelium is relatively 

 short; in those which are empty it is taller. Each cell contains a single 

 spheroidal nucleus which lies in the center of the cell, or somewhat 

 toward its basal extremity. This orderly disposition causes the nuclei, 

 when seen in sections of the follicle, to appear as a continuous row in 

 the wall of the alveolus, a disposition which is noticeable for its ex- 

 ceptional regularity. 



The cytoplasm of the epithelium is finely granular and decidedly 

 acidophilic. It usually contains some coarse granules and very small 

 fatty droplets, which generally occupy the extremities of the cells. Mi- 

 nute spheroidal granules which give the color reactions of colloid are 

 also found in the cytoplasm of the epithelial cells. Hiirthle (Arch. f. d. 

 ges. Physiol., 1894), by staining with the Biondi-Ehrlich mixture, suc- 

 ceeded in differentiating two types of cell, one lightly staining, the 

 'chief cells/ the other a darker colloid-containing type which he designated 

 as 'colloid cells.' These variations probably only represent different 

 stages of secretion in the same epithelial cell type. Minute intercellular 

 canaliculi occur at the angles between adjacent cells. 



In the thyroid of the opossum Bensley (Anat. Rec., 8, 9, 1914) also 

 describes two types of cells, namely, the usual epithelial cells and ovoid 

 cells. The latter hold a parietal position in the follicle; they are filled 

 with fine eosinophilic granules which give to these cells a character strik- 

 ingly similar to that of the acidophil cells of the anterior lobe of the hypo- 

 physis cerebri. He describes also large needle-shaped crystalloid bodies in 

 the epithelial cells similar to those in the interstitial and Sertoli cells of 

 the testis. 



The epithelium rests upon a very delicate reticular basement mem- 

 brane and is in close relation with the capillaries and lymphatic vessels 



