56 A Manual of Veterinary Physiology. 



many forms. Their essential construction consists of a 

 button which is pressed upon by each impulse of the heart, 

 and conveys the movement to an elastic air-chamber, which 

 transmits it to a recording lever. By this means we get a 

 graphic representation of the heart's impulse. 



The cardiograph demonstrates that the aortic valves close 

 slightly before the pulmonary. 



Capacity of Heart. — The quantity of blood in the heart 

 can only be ascertained approximately ; measuring the 

 capacity of the chambers is no guide. Munk states that 

 the capacity of the ventricle in a horse weighing 880 lbs. is 

 about 1-70 pints, equivalent to 2 35 lbs. of blood : each ven- 

 tricle contains one-thirtieth of the total blood, so that when 

 both contract one- fifteenth of the total blood is ejected 

 (M'Kendrick). My own observations on the capacity of the 

 heart have not as yet enabled me to make any general 

 statement. 



Colin gives the capacity of the left ventricle of the horse 

 at 1-76 pints, and states that at each systole two-thirds or 

 three-fourths of this quantity is injected into the aorta, viz., 

 1'172 pints to 1364 pints; the left ventricle at each con- 

 traction, according to this observer, forces into the aorta 

 about one-twenty-fifth of the total blood of the body. 



Colin gives the following table of capacities of right and 

 left ventricle : 



Right Ventricle. Left Ventricle. 



Pints. Pints. 



Small horse - 1-42 1 -29 



Medium size horse - 1*76 1*23 



Big horse - 3-34 2-36 



This is only a part of the table, the figures of which arc 

 found to vary widely. Measuring the capacity of the 

 heart is therefore fallacious, for in the above table each 

 side of the organ should have held the same quantity of 

 blood. 



Infra-cardiac Pressure. — Though both ventricles deliver 

 the same amount of blood, the pressure in each ca\ it \ is 

 different. Chauveau puts the systolic pressure in the left 



