FUNCTIONS OF THE BLOOD 271 



The Thyroid Gland. This organ lies in the neck on the sides 

 of the windpipe and consists usually of a right and a left lobe 

 united by a narrow isthmus across the front of the air-tube. It is 

 about thirty grams (two ounces) in weight; in the disease known 

 as goiter it is greatly enlarged and its structure altered. The 

 thyroid is dark red in color and very vascular, richly supplied 

 with nerves, and is subdivided by connective tissue into cavities 

 or alveoli, the largest of which are just visible to the unaided eye. 

 Each alveolus is lined by a single layer of cuboidal cells, and filled 

 by a glairy fluid known as the thyroid colloid. 



From the gland can be obtained, in addition to the usual or- 

 ganic compounds, a peculiar substance containing a large percen- 

 tage of iodine, and known as iodothyrin. This compound was 

 thought, when first discovered, to be the hormone of the gland, 

 but fuller study showed that iodothyrin as such is not the hormone 

 although it probably has to do in some way with it. Although 

 the chemistry of the hormone is not known its physiology can be 

 studied indirectly by observing the effect of depriving the Body 

 of it through removal of the gland, either experimentally or as 

 the result of disease. 



These studies show that the hormone of the thyroid gland has 

 a great deal to do with the proper carrying on* of those chemical 

 activities of living cells which constitute their "vital" processes 

 and which are grouped together under the term metabolism. 

 Lack of the hormone results in a condition of general malnutrition, 

 known as cachexia. Beside this general symptom certain special 

 tissues show very strikingly the effects of being deprived of the 

 thyroid hormone; these are the connective and nervous tissues. 

 In adults a condition known as myxedema is the result of such 

 deprivation; its most marked signs are swellings of the subcu- 

 taneous connective tissues, whereby the outlines of the Body are 

 much distorted; and distressing mental deterioration. Some- 

 times children are born in whom the thyroid gland fails to de- 

 velop properly; they grow into dwarfish, misshapen idiots. To 

 such a condition the name cretinism is applied. The sufferers 

 are called cretins. Thanks to the discovery that by simple feeding 

 of thyroid material the hormone can be supplied in ample quan- 

 tity, sufferers from myxedema and cretinism are now restored to 

 perfectly normal condition; although it is said that for the treat- 



