THE INTEGRATIVE ACTION OF THE VASCULAR SYSTEM 239 



centrated blood thus made to that in the vessels may increase 

 the number of circulating corpuscles by 20 per cent or more. 

 These corpuscles, of course, promptly become carriers of 

 oxygen and carbon dioxide, at a time when their services 

 are in demand. 



It is of interest to note that many of the changes in the 

 circulation described are a part of the bodily changes occur- 

 ring in profound emotional excitement. Respiration deepens, 

 the heart beats more rapidly, the arterial pressure rises, 

 the blood is shifted aw^ay from the stomach and intestines 

 to the heart and central nervous system and the muscles, 

 sugar is freed from the reserves in the liver, the spleen 

 contracts and adrenin is discharged from the adrenal 

 medulla. The key to these marvelous transformations in 

 the body is found in relating them to the natural accom- 

 paniments of fear and rage: running away in order to escape 

 and attacking in order to be dominant. Whichever the 

 action, a hfe-or-death struggle may ensue. The emotional 

 responses may be regarded as preparatory for that struggle, 

 adjustments which so far as possible put the organism in 

 readiness for meeting the demands which will be made 

 upon it. The secreted adrenin not only collaborates with 

 the sympathetic impulses, to the degree that they are 

 engaged in the adjustments, but it has the property of 

 extending the ability of fatigued muscle to continue at work. 

 All these wonderful arrangements which operate when we 

 engage in hard muscular exercise, and particularly when 

 there is attendant excitement, we can best understand by 

 reference to racial history. For myriads of generations our 

 ancestors have had to meet the exigencies of existence by 

 physical effort, perhaps in supreme effort. The struggle 

 for existence has been a nerve and muscle struggle. The 

 organisms in which the adjustments were most rapid and 

 most perfect had advantages over their opponents in which 

 the adjustments w^re less so. The functional perfections 

 had survival value, and we may regard the remarkable 

 arrangements for mobilizing the body forces, which are 

 displayed when intense muscular activity is required or 

 anticipated, as the natural consequences of a natural 

 selection. 



