172 CHEMICAL CORRELATION 



ing described have no ducts they are often referred to as 

 the ductless glands. 



Hormones Which Affect Basic Metabolism. — A 

 fact of great importance is that in normal animals so long 

 as the temperature continues constant the basic metabo- 

 lism goes on at a very uniform rate. The temperature here 

 referred to is the cell temperature and not the external 

 temperature. So in warm-blooded animals, whose cells 

 live in a uniform temperature, basic metabolism proceeds 

 without much alteration in rate, day in and day out. Evi- 

 dence has been obtained of recent years to prove that the 

 actual rate of basic metabolism is determined by the influ- 

 ence of a group of hormones, and the reason that it holds 

 at a fairly uniform level is because these hormones are 

 manufactured and poured out by their glands at a uni- 

 form rate. Should the glands become disordered so that 

 their output is either increased or diminished, the rate 

 of the basic metabolism is altered to correspond. 



Fig. 45. — The Thyroid CJhind, 7', shown in relation to the larynx, 

 L, and the trachea (windpipe) W. 



The Thyroid Hormone. — To illustrate the effect of 

 hormones on basic metabolism a single example, the best 

 known of all, will be cited. The thyroid gland lies at the 

 front and sides of the windpipe (Fig. 45) where it ordi- 

 narily fits into the contour of the neck and so is not no- 



