THE THYROID AND PARATHYROIDS 299 



He is inclined to think that there must be a duct opening 

 into the pharynx or the trachea. 



Santorini fails to find a duct, but still thinks that the thyroid 

 gland may be forced to expel its secretion by the contraction 

 of the overlying muscles and other causes. 



Haller, in his textbook, written in 1776, after discussing the 

 anatomy of the gland and detailing the fruitless attempts to 

 discover an efferent duct, says : " Alii Cl. viri, cum penitus de 

 inveniendo ductu desperassent, ad aliam omriino utilitatem 

 se converterunt. Liquorem peculiarem in ea glandula parari, 

 qui receptus venulis sanguini reddatur, quse lienis et thymi 

 fit utilitas, ipse Ruyschius autumavit." 



Thus, in the year 177\6, we have the thyroid, the thymus, 

 and the spleen classed together as glands without ducts, which 

 manufacture a special fluid, which is received into the veins, 

 and so returned to the general circulation. This, so far as it 

 goes, and, so far, at any rate, as it refers to the thyroid, is not 

 far different from the modern conception. 



Although from this time on the glandular nature of the 

 thyroid was universally conceded, and there w T as much specula- 

 tion as to the precise mode of secretion and the elimination of 

 the product from the vesicles into the circulation, yet the 

 active function of the secretion itself was for a long period not 

 the subject of any serious inquiry, and, indeed, the possibility 

 of its being of any great importance in the economy was 

 scarcely suspected. Thus, Cruveilhier, in 1834, states that the 

 use of the secretion of the thyroid is unknown, and about this 

 time Sir A. Carlisle supposed that the gland forms a protection 

 to the delicate organs of the voice, against the variations of the 

 external air. 



In 1844 Simon put forward a very interesting theory in 

 regard to the function of the thyroid, all the more interesting 

 as it has quite recently been revived. Simon considered that 

 the thyroid exercises a regulatory function on the blood- 

 supply to the brain, exerting also its secretory function in an 

 alternating manner with the substance of the brain. " What 

 diversion is to the stream of blood viewed quantitatively, 

 alternative secretion would be to the composition of the blood 

 viewed qualitatively ; and I should conceive that the use of 

 the thyroid gland, in its highest development, may depend on 

 the joint exercise of these two analogous functions. I should 



