INTERNAL SECRETION 239 



There are several organs once regarded as insignificant 

 which are now recognized as vital to the welfare of the 

 whole system. Among these the thyroid gland has at- 

 tracted particular interest. This is a small bilobed mass of 

 tissue situated in front of the trachea below the larynx. 

 It is one of several organs sometimes called ductless glands. 

 The term is more appropriate in this case than in some 

 others, since the microscope shows that the arrangement 

 of the cells is distinctly glandular. They surround small 

 recesses such as in typical glands would be in communica- 

 tion with an outlet or duct. Here, however, these cavities 

 are blind. They are seen to contain a viscid material, the 

 so-called colloid substance, which is evidently the product 

 of the secreting cells. Since there is no channel leading to 

 the exterior, the only possibility is that the distinctive 

 secretion shall enter the circulation either directly or by 

 way of the lymph. 



The thyroid gland is frequently enlarged and then gives 

 rise to the disfiguring swelling known as a goiter. Such 

 enlargements are not necessarily attended with general 

 disturbances of health, yet in many cases there are symp- 

 toms which can be referred to an excess of the active 

 product. Palpitation, breathlessness, extreme nervous- 

 ness, and marked loss of weight are likely to be observed. 

 The same manifestations follow the giving of overdoses of 

 thyroid extract. This has been employed for the correc- 

 tion of obesity, but it seems unwise to resort to a drug 

 so powerful and far reaching in its action for the treat- 

 ment of this condition. 



Just as there may be too much of the thyroid material 

 for the good of the subject, so there may be a serious de- 

 ficiency. The relative failure of the gland to function as 

 it should is the cause of a definite disease in human sub- 

 jects, and its removal from dogs is followed by a decline 

 if not by death. Young and growing animals are most 

 seriously affected. All the facts which have been gathered 

 support the belief that development and general well- 

 being depend to a considerable extent on the normal 



