THYROID AND ADRENAL GLANDS 33 



Each vesicle is lined by cuboidal epithelial cells, which secrete 

 a semi-gelatinous substance, colloid. 



It has long been known that the removal of the whole thy- 

 roid gland, including the parathyroid, occasioned marked in- 

 terference with nutrition and other changes, the chief of 

 which are disturbances of muscular coordination, possibly 

 convulsions, emaciation, apathy, and subsequent death. There 

 is no duct connected with the gland, and the secretion is 

 therefore an internal one. Very little is known of it except 

 that it is necessary to the maintenance of life. If a very little 

 of the gland be left, or if, after its complete removal, a small 

 bit of it be transplanted in some other part of the body, or if 

 the animal be fed on the thyroid extract or the fresh gland, 

 the characteristic symptoms do not ensue. 



The muscular disturbances direct the attention to the cen- 

 tral nervous system when an attempt is made to explain the 

 occurrences and it is not improbable that the effect of the 

 thyroid secretion is in some way exerted upon or through 

 the central system. It seems generally agreed that the thy- 

 roid does discharge a secretion into the blood and that it is 

 the withdrawal of some part of that secretion from the cir- 

 culation which is responsible for the remarkable train of 

 symptoms sequent upon its removal. This essential constit- 

 uent is regarded by some as being an agent which destroys 

 certain toxic principles in the blood, by others as being requi- 

 site to the metabolic functions in the body without destroy- 

 ing anything. .Baumann has isolated from the gland sub- 

 stance a material containing a large proportion of iodine, to 

 which he gives the name iodothyrin, and it is very probable 

 that this is one, at least, of the beneficial substances in the 

 thyroid secretion. 



Adrenal Glands. 



The adrenal gland or suprarenal capsules, resting upon 

 the upper ends of the kidneys, are ductless glands whose re- 



