148 THE THYROID, THE THYMUS, AND THE ADRENALS. 



direct causal relationship between the adrenals and oxidation 

 processes are sound, the thyroid must either be considered as 

 capable of playing a similar role in the organism, or it must 

 be so related to the adrenals as to, in a measure, govern their 

 functions. Analysis of the former proposition promptly shows 

 that it cannot prevail. As to any relationship between the 

 thyroid and the adrenals, all that can be said is that there 

 seems to exist a certain degree of functional connection be- 

 tween them, judging from the effects of their removal and the 

 character of their blood-supply. Indeed, the arteries of the 

 thyroid are remarkable in various ways, and particularly for 

 their number and size. Luschka 5 has estimated that the sum 

 of their transverse section equals the sectional area of the 

 internal carotid artery of the same side, so that nearly as 

 much blood passes through the four arteries supplying the 

 gland as goes to supply the brain through the vertebral and 

 internal carotid artery. The veins are correspondingly large, 

 and remarkable also for their number and free inosculation. 

 This is well shown in the annexed colored plate. Collecting, 

 as they do, the great mass of blood passed through the organ, 

 they are found to empty into channels that are suggestive by 

 their immediate anatomical relations: the internal jugular 

 and the innominate veins, which ultimately empty their blood 

 into the superior vena cava. Here again, therefore, we find 

 a loop with a large arterial trunk as the starting-point, a vena 

 cava as the main intermediate channel, and the heart as a 

 common distributing mechanism. As in the case of the supra- 

 renal secretion, the thyroid secretion must therefore penetrate 

 the pulmonary circuit, return to the heart, and then be dis- 

 tributed throughout the organism with blood. 



The features available as elements for an analysis of the 

 functions of the thyroid suggest that we are not dealing with 

 an intraglandular process having for its purpose to locally 

 destroy toxic substances. In the first place, the demonstrated 

 increase of vital activities, growth, metabolism, mental power, 

 etc., which thyroid extract procures would become unintel- 

 ligible, since its effect is peculiar to thyroid extractives: a fact 



B Luschka: Allen's "Anatomy," p. 366. 



