THE CIRCULATION OF THE BLOOD 181 



carbon dioxide from them, and is changed from a 

 scarlet to a bluish red color. The same venous return 

 of the blood occurs to the right auricle and the cycle 

 is repeated. It must be remembered that while the 

 venae cavse are filling the right auricle, the pulmonary 

 veins are at the same instant pouring their contents 

 into the left auricle. 



The blood is moved through the heart and blood- 

 vessels by a continuous, rhythmic, and automatic 

 contraction and relaxation of the heart muscle due 

 to an inherent power possessed by the heart of con- 

 verting potential energy stored up during the period 

 of rest into kinetic energy, i. e.,- heat and mechanic 

 motion. The rhythmic contraction wave of the 

 heart is carried on by means of a thin and distinct 

 bundle of muscle fibers the bundle of His or atrioven- 

 tricular. It commences in the right auricle near the 

 orifice of the Eustachian valve and passes to the wall 

 between the ventricles to end in the papillary muscles 

 of the ventricles. Disease or injury to these fibers 

 causes an interference with the muscular contraction 

 which begins in the auricle and extends to the ventricles. 

 This leads to a condition which arises as a result of the 

 auricle continuing to contract, and forces the blood into 

 the ventricles, allowing the blood to be continuously 

 pumped, while the ventricle not responding permits the 

 blood to collect, due to its inability to contract. This 

 condition is called Adams-Stokes sign or heart-block and 

 is fatal. When any portion of the heart contracts it 

 is called the systole, and relaxation, the diastole. The 

 heart having two cavities on each side, when their 

 walls contract and relax in succession we speak of 

 an auricular systole and diastole, and a ventricular 

 systole and diastole. 



The contraction systole of the heart muscle starts 

 as a wave in the great veins and then passes to the 

 base of the heart in both auricles, and extends rapidly 

 over the ventricles to the apex; during this period 



