180 UNCONSCIOUS NERVOUS OPERATIONS 



250. Effects of Vasomotor Action. The muscular action 

 of the arteries gives its general tone to the arterial system 

 and regulates the flow of blood in the whole body, and 

 this general tone is influenced by the central nervous sys- 

 tem. For instance, certain kinds of mental excitement 

 which affect the brain result in dilation of the arteries of 

 the face, which permits a more ample flow of blood to that 

 part, causing what is called Hushing. An opposite effect 

 may be produced by emotion, causing pallor. The action 

 is mainly reflex. So also in the case of the vessels of the 

 skin. When the temperature is low, they are constricted 

 and the surface becomes pale. As the temperature rises 

 the vessels dilate and the skin becomes flushed. While 

 these changes occur upon the surface, changes of a reverse 

 order take place in the viscera, and the temperature of the 

 body is thus largely regulated. Certain poisons in the 

 blood circulating through the brain affect the vasomotor 

 center, as when the blood is imperfectly oxygenated and 

 therefore impure, resulting sometimes in suffocation. 



251. Alcoholic beverages affect the delicate adjustment 

 of the vasoconstrictor arid vasodilator nervous forces 

 and may seriously interfere with the circulation. As pre- 

 viously stated, dilute alcohol causes the constrictor muscles 

 in the capillaries to relax so that the capillaries become 

 dilated, and by the continued use of alcoholic drinks they 

 may become permanently expanded. 



