240 SWALE VINCENT 



possible thaj in the experiments on dogs and cats, in which species the 

 parathyroids are in close proximity to the thyroid, a shred of thyroid tissue 

 was left behind in the operation for thyroidectomy. 



But it is certain that in certain pathological conditions the parathyroid 

 may contain vesicles resembling those of the thyroid, and the present 

 writer has collected Other evidence of functional relationship between 

 thyroid and parathyroid. (See Vincent (&), 1912.) 



Summary 



The Function of the Thyroid Gland. There can be no doubt that 

 the thyroid furnishes a substance or substances which are of the greatest 

 importance to the normal growth and metabolism of the body. One or 

 more of these substances appears to be an iodized derivative of protein 

 probably an iodized amin. The most striking of the activities displayed by 

 the active principle or principles is to stimulate katabolism, though there 

 are indications of an anabolic principle. Perhaps two separate active 

 substances may be concerned in these two antagonistic influences. 



There is some evidence that the secretion of the active substance is 

 under the control of the sympathetic nervous system. 



Is the activity of the substance secreted by the thyroid brought about 

 by immediate influence on the organs and tissues themselves, or is the 

 influence mediated, and effected through the agency of the nervous 

 system ? Each of these views may be supported by arguments of no mean 

 weight. 



The importance of the thyroid varies in different classes of animals. 

 Sheep quietly grazing in a field may, and do, get on very well without a 

 thyroid, while the hungry and active carnivore who preys upon them will 

 suffer severely from loss of the gland. 



Though we are beginning to understand something of the chemical 

 aspects of metabolism as influenced by the thyroid, the morphological 

 processes which are also influenced present problems which have received 

 so far relatively little attention. 



The current view of internal secretions in general and of the secretion 

 of the thyroid in particular, has changed somewhat since the word "hor- 

 mone" was invented. The modern conception is not so much that of a 

 series of excitants sent out to stimulate the activity of different organs 

 and tissues, as that of the existence of a certain essential minimal amount 

 of each active substance and the maintenance of some proportion between 

 the amounts of each (Paton). 



According to Kendall, the physiological action of the thyroid sub- 

 stance is probably that of a catalytic agent. The fundamental reactions 



