life: its nature, origin, and maintenance SCHAFER. 517 



language of poetry, and even of every day, the word ''heart" has 

 become synonymous with the emotions themselves. 



The involuntary muscle of the arteries has its action similarly bal- 

 anced. When its contraction is increased the size of the vessels is 

 lessened and they deliver less blood; the parts they sup])ly accord- 

 ingly become pale in color. On the other ?iand, when the contraction 

 is diminished the vessels enlarge and deliver more blood; the parts 

 which they supply become correspondingly ruddy. These changes in 

 the arteries, like the effects upon the heart, may also be produced 

 under the influence of emotions. Thus " blushing " is a purely phys- 

 iological phenomenon due to diminished action of the muscular 

 tissue of the arteries, wliilst the pallor produced by fright is caused 

 by an increased contraction of that tissue. Apart, however, from 

 these conspicuous effects, there is constantly proceeding a less 

 apparent but not less important balancing action between the two 

 sets of nerve fibers distributed to heart and blood vessels, which are 

 influenced in one direction or another by every sensation which we 

 experience, and even by impressions of which we may be wholly 

 unconscious, such as those which occur during sleep or anesthesia, or 

 which affect our otherwise insensitive internal organs. 



REGUI.ATIOX OF SECRETION AND BODY TEMPERATURE. 



A further instance of nerve regulation is seen in secreting glands. 

 Not all glands are thus regulated, at least not directly; but in those 

 which are the effects are striking. Their regulation is of the same 

 general nature as that exercised upon involuntary muscle, but it 

 influences the chemical activities of the gland cells and the out- 

 pouring of secretion from them. By means of this regulation a secre- 

 tion can be produced or arrested, increased or diminished. As with 

 muscle, a suitable balance is in this way maintained, and the activity 

 of the glands is adapted to the reciuiroments of the organism. Most 

 of the digestive glands are thus influenced, as are the skin glands 

 which secrete sweat. And by the action of the nervous system upon 

 the skin glands, together with its efl'ect in increasing or diminishing 

 the blood supply to the cutaneous blood vessels, the temperature of 

 our blood is regulated and is kept at the point best suited for mainte- 

 nance of the Ife and activity of the tissues. 



EFFECTS OF EMOTIONS ON SECRETION. 



The action of tlie nervous system upon the secretion of glands is 

 strikingly exemplified, as in the case of its action upon the heart and 

 blood vessels by the effects of the emotions. Thus an emotion of one 

 kind, such as the anticipation of food, will cause saliva to flow — "the 

 mouth to water;" whereas an emotion of another kind, such as fear 

 85360°— SM 1912 34 



