184 NORMAL HISTOLOGY. 



Chemical examination has revealed the presence of a substance 

 called " thyroiodin " in the alveoli of the thyroid gland. This is a 

 proteid containing a large amount of iodine. Its production by the 

 thyroid gland may be increased by feeding with substances contain- 

 ing considerable iodine or by administering iodide of potassium. 

 Injections of thyroiodin serve to mitigate the effects of thyroidec- 

 tomy, very much as do injections of thyroid extracts. It is by no 

 means clear, however, that the thyroiodin is the only substance 

 elaborated by the thyroid gland which may be of use to the tissues 



FIG. 159. 



o 



Section of the thyroid gland of a kitten two months old. (Kohn.) Showing the positions 

 of the outer and inner parathyroid bodies and a thymus follicle : t, thyroid gland ; p, 

 inner parathyroid; p', outer parathyroid; th, thymus follicle; a, portion of the section 

 showing the intimate relations between the thyroid and the inner parathyroid ; 6, por- 

 tion demonstrating a similar intimate relation between the thyroid and the tissues of the 

 thymus follicle. 



of other organs, or that the thyroid may not also remove injurious 

 substances from the circulation and thus indirectly benefit other 

 structures in the body. 1 



1 Attention is also called to the possibility that an excessive or morbid thyroid 

 secretion may cause symptoms of disease attributable to disturbances in the functions 

 of other organs, and may also occasion disturbances in nutrition. 



