270 VETERINARY PHYSIOLOGY 



former condition is indicative of an actively acting heart 

 with no great peripheral resistance the latter indicates that 

 the heart's action is weak in relationship to the arterial blood 

 pressure. 



(2) Does the wave fall slowly or rapidly ? Normally the 

 fall should not be so sudden as the ascent. When the 

 aortic valves are not properly closed the descent becomes 

 very rapid. 



(3) Are there any secondary waves to be observed ? The 

 only one of these which can be detected by the finger is the 

 dicrotic wave, and this only when it is well marked. When 

 it can be felt, the pulse is said to be dicrotic, and, as before 

 stated, this indicates an actively acting heart with an arterial 

 pressure low relatively to the strength of the ventricles. 



B. Capillary Pulse 



Normally there is no pulse in the. capillaries. Their thin 

 endothelial wall is not well adapted to bear such an inter- 

 mittent strain. If, however, the arterioles to a district are 

 freely dilated so that little resistance is offered to the escape 

 of blood from, the arteries, and if at the same time the out- 

 flow from the capillaries is not proportionately increased, 

 intermittent inflow and resistance to outflow are developed, 

 and a pulse is produced. Such a condition is seen in certain 

 glands during activity. 



C. Venous Pulse 



1. The absence of a general venous pulse has been already 

 explained. But just as in the capillaries so in the veins, a 

 local pulse may develop. 



2. In the veins entering the auricles a pulse occurs, but 

 a pulse having no resemblance to the arterial pulse, although 

 depending on the same three factors. 



Its form is indicated in fig. 125. 



Its features are to be explained as follows : 



Blood is constantly flowing into the great veins, pressed, 

 on from behind. When the auricles contract, the outflow 

 from these veins into the heart is suddenly checked, and con- 

 sequently the veins distend. At the moment of auricular 



