54 



THE CIRCULATION OF THE BLOOD 



The impulse is an index to the condition of the circulation. 

 Its frequency normally in an adult is about 72 times per 



FIG. 29. The left auricle and ventricle opened and part of their 



walls removed to show their cavities. (From Yeo 



after Allen Thompson.) 



i, right pulmonary vein cut short; i', cavity of left auricle; 3, 3", thick wall 

 of left ventricle; 4, portion of the same with papillary muscle attached; 5, the 

 other papillary muscles; 6, 6', the segments of the mitral valve, 7, in aorta is 

 placed over the semi-lunar valves. 



minute, in children it is higher, and it is more frequent in 

 woman than in man. Its frequency is affected by age, sex, 

 exercise, disease, drugs, and psychical causes, as fear, sor- 



