THE THYEOID GLAND 453 



the colloid mass, which is then adherent to the surface of the 

 lining epithelium by delicate thread-like processes; the colloid 

 thus acquires a deceptive appearance of extreme contraction, as if 

 its surface, except for occasional delicate strands, had been drawn 

 away from the epithelium. 



Occasionally a single large vacuole, often containing basophile 

 granules or crystalloid particles, occupies the center of the colloid 

 mass in the larger follicles ; at other times the colloid material 

 appears to be broken into minute spherules. In general, the ratio 

 of colloid content within the follicle, roughly stated, is in propor- 

 tion to the age of the individual. The follicles at the periphery 

 of the lobes of the gland are less fully distended than those in the 

 interior. 



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

 apparently normal thyroid, red blood cells and desquamated fol- 

 licular epithelium are frequently found, but never in large quan- 

 tity. Leucocytes are of less frequent occurrence and are more 

 rarely found in the human thyroid than in that of the lower 

 mammals. 



The follieular epithelium is typically cuboidal in shape ; in 

 young individuals it is somewhat taller than broad. In those fol- 

 licles 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 dispo- 

 sition which is noticeable for its exceptional regularity. 



The cytoplasm of the epithelium is finely granular and de- 

 cidedly acidophile. It usually contains some coarse granules and 

 very small fatty droplets, which are prone to occupy the extremi- 

 ties of the cells. Minute spheroidal granules which give the color 

 reactions of colloid are also found in the cytoplasm of the epithe- 

 lial cells. Hiirthle,* by staining with the Biondi-Ehrlich mixture, 

 succeeded 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. 



* Arch. f. d. ges. Physiol., 1894. 



