66 



THE HUMAN MECHANISM 



cells, from which it is discharged by nervous impulses. Like 

 the thyroids, the adrenals have no ducts ; but the cells of 

 the gland come into very close relation with the unusually 

 rich network of blood capillaries into which the adrenaline is 

 discharged when the gland is stimulated by its nerves. 



Once in the blood, ad- 

 renaline produces profound 

 effects in many organs of 

 the body. Among these may 

 be mentioned a decrease 

 in the blood supply to the 

 digestive organs; a change 

 in the beat of the heart; 

 an increased flow of blood 

 through the brain, the skele- 

 tal muscles, and, to a less 

 extent, the skin; the dis- 

 charge of sugar into the 

 blood by the liver; and an 

 increase in the number of 

 the red blood corpuscles 



FIG. 37. Diagrams of external (A) and ( see P* 136). 



internal (B) secretion It is a most significant 



fact that many if not most 

 of the reactions of the or- 

 ganism to adrenaline are the 

 very reactions which are 

 needed in times of great 

 muscular exertion. For example, the shifting of the blood 

 from digestive organs to the working muscles and to the 

 brain, which is thereby rendered more alert; the supply of 

 increased quantities of sugar to serve as power for muscular 

 work ; the assistance to the heart, which is called upon at such 

 times to pump more blood; the augmented oxygen-carrying 

 capacity of the blood by increase of its red corpuscles all 



The passage of food material from the 

 capillaries into the gland cells is repre- 

 sented by the arrows with broken lines; 

 the path of discharge of the secretion, in A 

 into the duct and in B into the blood, is in- 

 dicated by the arrows with unbroken lines 



