f>8 A Manual of Veterinary Physiology. 



pulse rate. The more rapid the pulse, the greater the quan- 

 tity of blood in circulation. 



The Velocity of the Blood varies in the arteries, capillaries, 

 and veins, being greatest in the former, least in the capil- 

 laries, and rising again in the veins. The velocity of blood- 

 How is due to the width of the bed formed by the vessels ; 

 as the arterial system expands, the velocity diminishes. In 

 passing through the capillaries, with their immense network, 

 the velocity is at a minimum ; in passing towards the heart 

 the vessels are reduced in number, hence the bed is less, and 

 the velocity accordingly increases. The cause of the flow 

 throughout the entire system is the contraction of the left 

 ventricle, aided by certain accessory movements, which will 

 shortly be alluded to. The velocit}' does not depend upon 

 the blood pressure, but upon the force of the heart and the 

 peripheral resistance. 



The vascular system has been compared to two cones 

 placed base to base, the apex of one being the left ventricle, 

 of the other the right auricle : where the bases of the two 

 cones meet is the capillary network ; the sectional area of 

 this has been estimated as 500 times greater than that of 

 the aorta, whilst the passage of blood through it, owing 

 to the resistance experienced, is 500 times slower than in 

 the aorta (Volkmann). 



According to the same authorit}', the velocity of blood 

 in the carotid of the horse is from lis inches to 15*75 

 inches per second ; in the metatarsal artery of the horse 

 2*2 inches per second ; and in the jugular vein 8*85 inches 

 per second. Chauvcau found in the great arteries near the 

 heart a velocity of 20-47 inches per second during systole ; 

 at the beginning of diastole 866 inches per second, and 

 during the pause 59 inches per second (M'Kendrick). 



The velocity of the blood is increased l>\ each systole of 

 the ventricle, and in arteries by each expiration ; inspira- 

 tion, on the other hand, does not retard the flow of blood 

 in the thick- walled., highly-distended arteries, but assists 

 it in the veins. The velocity of the blood is greater in 

 the pulmonary than in the systemic capillaries, while the 



