THE THYKOID AND PARATHYROIDS 273 



be treated with acetic acid until considerable swelling occurs, 

 and then, after washing, be treated with sulphuric acid, a violet 

 coloration is perceived (Adamkiewicz's reaction). 



The colloid masses are not dissolved in boiling water, but 

 are coagulated. The colloid is also coagulated by the other 

 ordinarily used fixing and hardening reagents. These are 

 alcohol, inorganic acids, solutions of metallic salts, and picric 

 acid. 



Langendorff considers that the colloid masses are composed 

 either of protein or a substance containing a large proportion of 

 protein. Mucin is not present, as the reaction to acetic acid 

 shows. The protein can hardly be alkali-albuminate, since it 

 coagulates on heating. It may possibly be an alkali albumin 

 modified by containing abundance of sodium chloride. The 

 reactions do not allow of the supposition that any appreciable 

 amount of globulin is present. 



The staining power of the colloid is considerable. With 

 picrocarmine the colloid appears bright yellow. If one stains 

 with ammoniacal carmine the colloid takes on the carmine 

 tint very slightly. Eosin and the rest of the aniline dyes 

 stain the colloid powerfully. After treatment with osmic 

 acid or mixtures containing it, the colloid masses are stained 

 dark ; the reduction is particularly marked if one stains 

 for a short time with Ehrlich's hsematoxylin. After long 

 treatment with logwood the colloid becomes bluish-grey or 

 violet. 



The consensus of opinion at the present time is that the 

 colloid material arises as a secretion from the epithelial cells 

 lining the vesicle. The epithelium consists of cells having all 

 the characters of true glandular cells, and as in these, the 

 secretion is formed as specific granules in the reticular proto- 

 plasm. 



In the foetus the structure of the thyroid resembles that of 

 the adult, while in the new-born it is stated to be quite different. 

 It is said that after birth and for some weeks or months, the 

 vesicles shrivel up and the colloid disappears, and the gland 

 consists of elongated or rounded heaps of epithelial cells, closely 

 pressed together. It is possible that this change after birth is 

 pathological. 



