22 



MAN 



muscles to flex the bones of the legs into a position best to 

 maintain or regain the equilibrium of the body. 



Circulation of the Blood. We have seen that practi- 

 cally every part of the body is crowded with nerves connected 

 with the brain ; it is equally crowded with blood-vessels 

 connected with the heart. Space will not allow a detailed 

 examination of the composition of blood, but it is easy 



to recognise 

 its impor- 

 tance. Sup- 

 pose one 

 were to 

 bind an arm 

 very tightly 

 near the 

 shoulder, 

 the result 

 would 

 speedily be 

 discernible. 

 Below the 

 bandage the 

 flesh would 

 grow cold, 

 feeling 

 would be 

 blunted, 

 and move- 

 ment of the 

 arm would 



become 



heavy and 



clumsy. If the ligament were sufficiently tight and sus- 

 tained long enough, the arm would become dead and 

 useless. Why ? Not because we have deprived the arm 

 of its blood, for its vessels might be full to bursting ; 

 but because we have interfered with its circulation. The 

 heart is a pump, which forces the life-giving fluid through 

 its greatest artery, the aorta, which branches out again 

 and again into ever smaller arteries, until the tubes are 



DISSECTION OF LEFT SIDE OF HEART OF MAN, 

 SHOWING VALVES. 



L.V. Left Ventricle; L.A. Left Auricle; m.v. Mitral Valve; 



p.a. Pulmonary Artery ; s.v. Semilunar Valves of Pulmonary 



Artery; ao. Aorta; s.v'. Semilunar Valves of Aorta. 



