CHAP. II.] RE-CONVERSION OF VENOUS BLOOD. 117 



(right) side, through a small door-way, or valve, 

 which opens only inwards, the door being too large 

 for the door-way. By the way, these valves are 

 very numerous in the animal system, principally 

 as regards the circulation of blood in the veins ; 

 and the reader will do well to recollect, when we 

 speak of valves in future, the illustration just given 

 by comparing the same to a door-way, which bears 

 a near resemblance to the valve. In the perform- 

 ance of this office, the heart may be said to have 

 three several motions belonging to it: 1st, a quick 

 one, by the contractions of the smaller chambers 

 upon their contents : 2d, the contractions of each 

 large chamber upon its contents, being just half the 

 number of throbs made by the first mentioned : and, 

 3d, the vibration or tremor of the whole heart, in 

 consequence of those other motions. 



Well, on the right side still, the large chamber 

 being filled with venous blood through the valve, 

 or door-way, from the small one, becomes in like 

 manner irritated so as to contract upon its contentsj 

 and to drive it out somewhere or other. Back to 

 the small chamber it cannot possibly go ; the valve 

 does not open that way, as we have just now said ; 

 and, therefore, it issues with much more force through 

 another valve into a short artery, which soon opens 

 into two, like the letter Y, the heart being supposed 

 at the bottom of the letter. Up rushes the blood to 

 the top of the two branches — where it meets with — 

 What ? What do you think it meets with, gentle 

 Header ? 



