380 HUMAN PHYSIOLOGY 



use, but the temporary concentration of the sugar in 

 the blood may be purposeful. The wise interpreter 

 whose exposition we are following points out that extra 

 fuel of the preferred kind is thus offered to the muscles. 

 So they are made unusually responsive to stimulation 

 through their nerves at the same time that they are 

 provided with a liberal allowance of sugar for oxidation. 



An odd alteration in the blood which can be noted 

 directly after excitement is a shortening of the time re- 

 quired for coagulation. The reduction is very marked. 

 The suggestion is that an exciting situation is one 

 which may be followed by conflict and loss of blood. 

 The chances of victory and survival will be better for the 

 combatant whose blood most promptly staunches its 

 own flow. 



Adrenin plays a part in securing all the valuable adapt- 

 ive changes that have been enumerated. It would not 

 be wholly correct to say that it can, without assistance, 

 cause them all, for its influence is intimately combined 

 with others of a nervous order. There are certain nerve 

 paths in the body which can .be stimulated with the 

 result that the following effects are produced: quickening 

 of the heart, dilation of the pupils, contraction of the 

 abdominal blood-vessels, erection of the hairs, sweating, 

 and the discharge of adrenin. Adrenin itself can produce 

 most of the associated reactions. It may be conceived 

 that during the experience of emotion impulses from the 

 brain traverse these paths, adrenin is added to the blood, 

 and the hormone perpetuates and extends effects which 

 were at first nervous in origin. 



It may be remarked that although these bodily 

 changes . are admirably suited to the needs of animals 

 and cave men, they are not so well suited to the restrained 

 life of civilization. When we experience emotion we try 

 to refrain from manifesting it violently. It is not un- 

 likely that the physical accompaniments are harmful 

 when no application of them is made. Yet, as was said 

 in Chapter XII, a life deficient in emotion is a life lacking 



