CHAPTER XVIII. DAN WANTS TO KNOW HIMSELF.

Dan Clemens had taken at the first very little interest in the peculiar¹ 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 enraptured² with the skill, firmness, and tender feeling manifested by Rich, spent a great deal of time at the dissecting³ table, and manifested a strong desire to obtain, at least, some general knowledge in respect to the mechanism⁴ of his own frame.

One evening he was seated in the harness-room, watching Rich, who was examining the stump⁵ 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 tourniquet⁶ to compress the vessels⁷ and stop the[Pg 206] circulation, then cut through the flesh, saw off the bones, and put ligatures on the ends of the arteries⁸."

"What is it makes the great difference between the arteries and the veins⁹, so that folks say, if you cut an artery¹¹, 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 appendages¹², 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 dilates¹³ with great force. It is not dependent upon the will, but operates in virtue¹⁵ of a natural law. Through the middle of the heart, from the base to the summit, runs a partition, leaving a chamber¹⁶ on each side, between which there is no direct communication: they are distinguished¹⁷ by the terms right and left auricles. In addition to this, there is a cross parting on each side, thus making four chambers¹⁸, 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 vein¹⁰ of the body, that, in connection with the others, brings back the blood from the extremities¹⁹, 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 penetrated²¹ by the great artery, called the great aorta²². 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 obstruct²³ 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 by the pulmonary veins, distributes it over the trunk and limbs, branching in every direction, the divisions gradually becoming smaller and smaller as they approach the extremities: here they communicate with the extremities of the veins which bring back the blood to the right auricle. So much for the aqueducts; now we will look at the action of the force-pump itself. The heart is a hollow muscle. All the valves and division walls we have been talking about are muscular in their texture²⁴, and moved by a network of muscles and minute tendons, tough and elastic²⁵, like the gizzard of a fowl²⁶, and capable of contraction²⁷ and expansion. We will suppose the right auricle to be full of blood that has been brought by the veins from the fingers, toes, the substance of the heart itself, the lungs, and the liver, and poured into it. This blood is dark-colored; called black blood. It has washed the whole body. The instant it enters the auricle, that organ contracts and forces[Pg 210] it into the ventricle below it; the valve holds it there: then the ventricle contracts and forces it into the pulmonary artery; the valve of the artery holds it there: the auricle expands, fills, again contracts, fills the ventricle, that, in its turn, forces the blood into the artery, and thus, by successive leaps, it passes into and through the lungs, enters the pulmonary veins, and is by them brought back to the left auricle. It is now no longer black blood, but bright, red, arterial blood: before it was venous."

"What makes it red?"

"I don't know. It is supposed by being brought in contact with the air in the cells of the lungs. When the auricle receives this red blood, it contracts, forces it into the left ventricle beneath, then the ventricle in its turn contracts, forces it into the main artery, and by this and its branches it is carried to the extremities, to come back in one continual round, as long as life lasts. It is life; for the moment the heart ceases to contract and dilate¹⁴, insensibility takes place, and death instantly follows."

"It seems to me that the left side of the heart has a great deal more work to do than the right, for the left has to force the blood into the main artery, and all over the body, to the toes, the fingers, the brain: but the right ventricle only has to force it through the lungs that are close by, touch the heart, and it is a short route."

[Pg 211]

"True, and for this reason, the muscles of the left ventricle, which force the red blood of the great circulation through the main artery, are much more numerous and stronger than those of the right, which has so much less work to perform. It is the powerful contraction of the muscles of the left ventricle, causing the point of the heart to strike the fifth or sixth rib²⁰, that creates the throb²⁸ you can feel; they exert power enough to send all the blood of the body through the heart twenty-three times in an hour."

"I had no idea matters were going ahead inside of me at that rate."

"You must bear in mind that I have described these things separately, but in the order of nature, it is quite another matter. The red blood from the lungs arrives at the left, and the black blood from the veins at the right auricle at the same instant; both auricles contract at once, and force the blood into their respective ventricles; both ventricles contract together and force the blood into the arteries; and thus it goes on in a person of the feeblest pulse; these alternate motions occupy, when in a state of health, but a second; the pulse at your wrist is the throb of the artery, the stroke of the heart. What do you suppose now is the force of that stroke, when the left ventricle contracts?"

"I'm sure I don't know."

"Well, the blood has been known to spurt²⁹ more[Pg 212] than five feet from the artery of the neck (carotid) when first cut. You see, now, why it is so dangerous to wound a large artery: the blood spurts³⁰ at every stroke of the heart, while in the veins there is no such pressure or direct connection; besides, as the veins are designed not to carry the blood from the heart, but to bring it back, they are also furnished with numerous valves that favor the flow of blood towards the heart, but not from it."

"There is one thing I can't understand. When a man's leg is cut off, all the arteries and veins cut, how does the blood get back to the heart when the ends of the arteries are tied, and there is no communication between them and the veins?"

"By a provision of nature, there are many minute twigs³¹ and branches given off by the arteries all along their course, scarcely observable when the circulation is in its normal state, that are connected with veins equally small; those become enlarged by pressure, and renew the connection."

"It seems to me, Mr. Richardson, that the heart is like two pumps in two wells, side by side, only one throws a bigger stream than the other, and with more force."

"Ay, Daniel; but your mother's pump bears no comparison to the heart. During the time I have been with her, the spear has worn off, the boxes have been new leathered, and the cracks in the pump that sucked air have been covered with putty[Pg 213] and lead; but this pump runs eighty, and sometimes a hundred years without the pause of a second."

"Why don't the muscles of the heart get tired, just as my legs do, and want to rest?"

"They do rest, and just as long as they work; rest a second, and work a second, day and night. The other muscles are in a state of tension all day, and then rest at night."

"Well, I mean to know how I am made up, before I am much older."

1 peculiar   

adj.古怪的，异常的；特殊的，特有的

参考例句：

• He walks in a peculiar fashion.他走路的样子很奇特。
• He looked at me with a very peculiar expression.他用一种很奇怪的表情看着我。

2 enraptured   

v.使狂喜( enrapture的过去式和过去分词 )

参考例句：

• He was enraptured that she had smiled at him. 她对他的微笑使他心荡神驰。 来自《简明英汉词典》
• They were enraptured to meet the great singer. 他们和大名鼎鼎的歌手见面，欣喜若狂。 来自《简明英汉词典》

3 dissecting   

v.解剖（动物等）( dissect的现在分词 )；仔细分析或研究

参考例句：

• Another group was dissecting a new film showing locally. 另外一批人正在剖析城里上演的一部新电影。 来自辞典例句
• Probe into Dissecting Refraction Method Statics Processing under Complicated Surface Conditions. 不同地表条件下土壤侵蚀的坡度效应。 来自互联网

4 mechanism   

n.机械装置；机构，结构

参考例句：

• The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
• The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。

5 stump   

n.残株，烟蒂，讲演台；v.砍断，蹒跚而走

参考例句：

• He went on the stump in his home state.他到故乡所在的州去发表演说。
• He used the stump as a table.他把树桩用作桌子。

6 tourniquet   

n.止血器，绞压器，驱血带

参考例句：

• Twist the tourniquet tighter.把止血带扎紧点。
• The tourniquet should occlude venous and lymphatic return.止血带应阻断静脉及淋巴回流。

7 vessels   

n.血管( vessel的名词复数 )；船；容器；（具有特殊品质或接受特殊品质的）人

参考例句：

• The river is navigable by vessels of up to 90 tons. 90 吨以下的船只可以从这条河通过。 来自《简明英汉词典》
• All modern vessels of any size are fitted with radar installations. 所有现代化船只都有雷达装置。 来自《现代汉英综合大词典》

8 arteries   

n.动脉( artery的名词复数 )；干线，要道

参考例句：

• Even grafting new blood vessels in place of the diseased coronary arteries has been tried. 甚至移植新血管代替不健康的冠状动脉的方法都已经试过。 来自《简明英汉词典》
• This is the place where the three main arteries of West London traffic met. 这就是伦敦西部三条主要交通干线的交汇处。 来自《简明英汉词典》

9 veins   

n.纹理；矿脉( vein的名词复数 )；静脉；叶脉；纹理

参考例句：

• The blood flows from the capillaries back into the veins. 血从毛细血管流回静脉。 来自《简明英汉词典》
• I felt a pleasant glow in all my veins from the wine. 喝过酒后我浑身的血都热烘烘的，感到很舒服。 来自《简明英汉词典》

10 vein   

n.血管，静脉；叶脉，纹理；情绪；vt.使成脉络

参考例句：

• The girl is not in the vein for singing today.那女孩今天没有心情唱歌。
• The doctor injects glucose into the patient's vein.医生把葡萄糖注射入病人的静脉。

11 artery   

n.干线，要道；动脉

参考例句：

• We couldn't feel the changes in the blood pressure within the artery.我们无法感觉到动脉血管内血压的变化。
• The aorta is the largest artery in the body.主动脉是人体中的最大动脉。

12 appendages   

n.附属物( appendage的名词复数 )；依附的人；附属器官；附属肢体（如臂、腿、尾等）

参考例句：

• The 11th segment carries a pair of segmented appendages, the cerci. 第十一节有一对分节的附肢，即尾须。 来自辞典例句
• Paired appendages, with one on each side of the body, are common in many animals. 很多动物身上有成对的附肢，一侧一个，这是很普遍的现象。 来自辞典例句

13 dilates   

v.（使某物）扩大，膨胀，张大( dilate的第三人称单数 )

参考例句：

• Gas dilates the balloon. 气体使汽球膨胀。 来自《现代英汉综合大词典》
• Exercise dilates blood vessels on the surface of the brain. 运动会使大脑表层的血管扩张。 来自辞典例句

14 dilate   

vt.使膨胀，使扩大

参考例句：

• At night,the pupils dilate to allow in more light.到了晚上，瞳孔就会扩大以接收更多光线。
• Exercise dilates blood vessels on the surface of the brain.运动会使大脑表层的血管扩张。

15 virtue   

n.德行，美德；贞操；优点；功效，效力

参考例句：

• He was considered to be a paragon of virtue.他被认为是品德尽善尽美的典范。
• You need to decorate your mind with virtue.你应该用德行美化心灵。

16 chamber   

n.房间，寝室；会议厅；议院；会所

参考例句：

• For many,the dentist's surgery remains a torture chamber.对许多人来说，牙医的治疗室一直是间受刑室。
• The chamber was ablaze with light.会议厅里灯火辉煌。

17 distinguished   

adj.卓越的，杰出的，著名的

参考例句：

• Elephants are distinguished from other animals by their long noses.大象以其长长的鼻子显示出与其他动物的不同。
• A banquet was given in honor of the distinguished guests.宴会是为了向贵宾们致敬而举行的。

18 chambers   

n.房间( chamber的名词复数 )；（议会的）议院；卧室；会议厅

参考例句：

• The body will be removed into one of the cold storage chambers. 尸体将被移到一个冷冻间里。 来自《简明英汉词典》
• Mr Chambers's readable book concentrates on the middle passage: the time Ransome spent in Russia. Chambers先生的这本值得一看的书重点在中间：Ransome在俄国的那几年。 来自互联网

19 extremities   

n.端点( extremity的名词复数 )；尽头；手和足；极窘迫的境地

参考例句：

• She was most noticeable, I thought, in respect of her extremities. 我觉得她那副穷极可怜的样子实在太惹人注目。 来自辞典例句
• Winters may be quite cool at the northwestern extremities. 西北边区的冬天也可能会相当凉。 来自辞典例句

20 rib   

n.肋骨，肋状物

参考例句：

• He broke a rib when he fell off his horse.他从马上摔下来折断了一根肋骨。
• He has broken a rib and the doctor has strapped it up.他断了一根肋骨，医生已包扎好了。

21 penetrated   

adj. 击穿的，鞭辟入里的 动词penetrate的过去式和过去分词形式

参考例句：

• The knife had penetrated his chest. 刀子刺入了他的胸膛。
• They penetrated into territory where no man had ever gone before. 他们已进入先前没人去过的地区。

22 aorta   

n.主动脉

参考例句：

• The abdominal aorta is normally smaller than the thoracic aorta.腹主动脉一般比胸主动脉小。
• Put down that jelly doughnut and look carefully at this aorta.放下手头上的东西，认真观察这张大动脉图片。

23 obstruct   

v.阻隔，阻塞(道路、通道等)；n.阻碍物，障碍物

参考例句：

• He became still more dissatisfied with it and secretly did everything in his power to obstruct it.他对此更不满意，尽在暗里使绊子。
• The fallen trees obstruct the road.倒下的树将路堵住了。

24 texture   

n.(织物)质地；(材料)构造；结构；肌理

参考例句：

• We could feel the smooth texture of silk.我们能感觉出丝绸的光滑质地。
• Her skin has a fine texture.她的皮肤细腻。

25 elastic   

n.橡皮圈，松紧带；adj.有弹性的；灵活的

参考例句：

• Rubber is an elastic material.橡胶是一种弹性材料。
• These regulations are elastic.这些规定是有弹性的。

26 fowl   

n.家禽，鸡，禽肉

参考例句：

• Fowl is not part of a traditional brunch.禽肉不是传统的早午餐的一部分。
• Since my heart attack,I've eaten more fish and fowl and less red meat.自从我患了心脏病后，我就多吃鱼肉和禽肉，少吃红色肉类。

27 contraction   

n.缩略词，缩写式，害病

参考例句：

• The contraction of this muscle raises the lower arm.肌肉的收缩使前臂抬起。
• The forces of expansion are balanced by forces of contraction.扩张力和收缩力相互平衡。

28 throb   

v.震颤，颤动；(急速强烈地)跳动，搏动

参考例句：

• She felt her heart give a great throb.她感到自己的心怦地跳了一下。
• The drums seemed to throb in his ears.阵阵鼓声彷佛在他耳边震响。

29 spurt   

v.喷出；突然进发；突然兴隆

参考例句：

• He put in a spurt at the beginning of the eighth lap.他进入第八圈时便开始冲刺。
• After a silence, Molly let her anger spurt out.沉默了一会儿，莫莉的怒气便迸发了出来。

30 spurts   

短暂而突然的活动或努力( spurt的名词复数 )； 突然奋起

参考例句：

• Great spurts of gas shoot out of the sun. 太阳气体射出形成大爆发。
• Spurts of warm rain blew fitfully against their faces. 阵阵温热的雨点拍打在他们脸上。

31 twigs   

细枝，嫩枝( twig的名词复数 )

参考例句：

• Some birds build nests of twigs. 一些鸟用树枝筑巢。
• Willow twigs are pliable. 柳条很软。