532 CIRCULATION OF BLOOD AND LYMPH 



4. Second negative wave. At the time of opening of the semi- 

 lunar valves. Due to descent of the base of the ventricle, causing 

 dilatation of auricle. 



5. Second systolic wave (positive), v wave. Latter part of 

 systole. Due to gradual filling of auricle and at the end to the 

 return of the base of the ventricle to its diastolic position. 



6. Postsystolic (third) negative wave begins at moment of 

 opening of the a-v. valves. Due to emptying of auricular blood 

 into ventricle. 



Other waves have been described, especially one in the dias- 

 tolic phase of the ventricular beat, which is known as the h wave 

 (Hirschf elder) or 6 wave (Gibson). This wave occurs between 

 the v and the a wave and is seen most frequently and distinctly in 

 the case of hearts with a slow rate of beat. The usual explanation 

 of this wave is that it is due to the very sudden distention of the 

 ventricles by the inflowing blood. The rise in intra ventricular 

 pressure thus produced brings the auriculoventricular valves 

 suddenly into a position of closure and causes a momentary posi- 

 tive wave in the auricles and great veins. For the variations in 

 the form of the venous pulse under pathological conditions of the 

 heart, reference must be made to clinical literature.* 



* See Hewlett, "Journal of Medical Research," 17, 1907; "Journal of 

 the Amer. Med. Assoc.," 51, 1908, and Hirschfelder, " Diseases of the 

 Heart and Aorta," Philadelphia, 1910 



