Dan Clemens had taken at the first very little interest in the peculiar studies and experiments of his teacher; indeed, they were to him, a kindly-affectionate boy, rather revolting; but after the successful operation upon Rover, his feelings underwent a complete change; he was enraptured with the skill, firmness, and tender feeling manifested by Rich, spent a great deal of time at the dissecting table, and manifested a strong desire to obtain, at least, some general knowledge in respect to the mechanism of his own frame.

One evening he was seated in the harness-room, watching Rich, who was examining the stump of Rover's leg, that had become sore from the pressure of the wooden substitute, and devising some way to remedy it, when he suddenly exclaimed,—

"Mr. Richardson, how do they cut off a man's leg?"

"Very much as I did that dog's; only they use a tourniquet to compress the vessels and stop the[Pg 206] circulation, then cut through the flesh, saw off the bones, and put ligatures on the ends of the arteries."

"What is it makes the great difference between the arteries and the veins, so that folks say, if you cut an artery, you'll bleed to death in no time. But they never speak so about veins; it's always arteries."

"I can't explain it to you, without telling you something about the heart, to start with."

"Well, tell me. O, do tell me, please."

"You saw the hog's heart I had the other day. Do you remember how it looked?"

"It looked something like an egg little end up."

"Well, a hog's heart is very much like a man's, so that one will do to represent the other. You noticed that it was smooth, and stood out about its whole bigness clear from everything, except at the base, where it joined the body?"

"Yes, sir."

"On each side of the base are two appendages, wrinkled, and shaped like an ear, denoting cavities within called from them the auricles, and into these cavities run several tubes that connect them to the parts adjacent. They are called auricles because they look so much like an ear."

"I know what they are. I saw the butcher cut them off, when he trimmed our hog's harslet: he called them deaf ears, and said they were poison."

"The heart is a hollow muscle, that contracts[Pg 207] and dilates with great force. It is not dependent upon the will, but operates in virtue of a natural law. Through the middle of the heart, from the base to the summit, runs a partition, leaving a chamber on each side, between which there is no direct communication: they are distinguished by the terms right and left auricles. In addition to this, there is a cross parting on each side, thus making four chambers, the two upper retaining the name of auricles, the two lower denominated ventricles.

"I will now explain to you the use of all this. The right auricle opens into the large trunk vein of the body, that, in connection with the others, brings back the blood from the extremities, after the arteries have distributed it. It has also another opening into the right ventricle below it. The auricle on the other side of the partition (the left) is pierced by four veins that enter the lungs, called pulmonary veins, and also by another passage communicates with the ventricle beneath it. Now let us talk about ventricles. The right ventricle is entered by the great pulmonary artery that carries all the blood in the body through the lungs. The left ventricle is penetrated by the great artery, called the great aorta. In each of these cross partitions, there are valves that will permit blood to pass from the auricles into the ventricles, but not to return. There are also valves at the roots of the arteries that permit the[Pg 208] blood to go from the heart into the arteries, but not to return. There are no valves at the roots of the veins that enter the auricles, nothing to obstruct the flowing of the blood from them into the auricles. Thus the roots of the veins arise from the auricles, and the roots of the arteries from the ventricles. Do you understand this description, because it is the foundation of all that follows—understand what a valve is?"

"Yes, sir; the clapper in our pump-box is a valve; it lets the water come up out of the well into the pump, but it won't let a drop go back."

"Well said; just so the valves in the partings of the heart permit the blood to pass from the auricles into the ventricles, but not to go back; thus, also, the valves placed at the roots of the arteries permit the passage of the blood from the ventricles into the arteries, but not the return of it to the heart. Do you understand this?"

"Yes, sir."

To make it more evident, Rich drew the heart, the veins, and the arteries entering it, with chalk, and the main branches of both.

"Now let us, for the clearer perception of what you wish to know, consider the march of the blood: and we might as well begin at the heart as anywhere."

"I think I can understand it better to commence there."

"From the right ventricle of the heart, springs[Pg 209] the pulmonary artery, which, separating into several branches, some of them not larger than hairs, carries the blood into all portions of the lungs, where they communicate with the terminations of the pulmonary veins, which, receiving the blood from the arteries, bring it back to the left auricle, uniting, as they approach the heart, into four large veins, called the pulmonary veins. From the left ventricle rises the main artery (or great aorta), which, receiving all the blood of the body poured into it............