THE BLOOD AND CIRCULATION 327 



long intervals only. The heart must be trained by well 

 regulated exercise to respond to all demands upon it. 



Regulation of heart action. — If a heart is cut off from 

 the living body it goes right on beating for a while. This 

 shows that cardiac or heart muscle differs from any other, 

 since it does not require an impulse from the central ner- 

 vous system to keep up its movements. 



Inhibitory and acceleration fibers. — The heart is, however, 

 supplied with two kinds of nerve fibers which regulate the 

 force and rate of the heart beat. The acceleration fibers 

 stimulate the heart to beat stronger and faster. The inhibi- 

 tory fibers slow the beat and lessen its strength. The 

 nerve centers where these fibers originate are believed to 

 be stimulated by the products of muscular activity resulting 

 from metabolism. Thus the activity of one organ regulates 

 the activity of another and the work of one is adjusted to 

 the demands of the other. 



Treatment of cuts and bruises. — In cases of injury 

 where the skin is broken, special precaution must be taken 

 in dressing the wound to prevent bacteria or other 

 microbes from infecting the wound and thus gaining entrance 

 into the circulation. Lockjaw and blood poisoning are 

 diseases that result from such infection. The first thing 

 to do, therefore, is to wash the wound and the skin about 

 the wound with a clean cloth or bit of absorbent cotton and 

 soap, and apply a disinfectant such as weak corrosive subli- 

 mate (i part to 100 parts water) or peroxide of hydrogen. 

 If a large artery is cut, the high pressure in the arteries 

 will cause the blood to flow out in spurts. In this case, 

 the artery must be bandaged between the wound and the 

 heart. To do this press the artery firmly with the finger 

 imtil the blood ceases to flow. Then have someone tie 

 a knot in a handkerchief or bandage and twist this loosely 

 about the limb with the knot applied over the artery. Place 

 a stick under the bandage, and twist it until the constriction 



