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Chapter XIII
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The Third Position is Confirmed: And the Circulation of the Blood is Demonstrated from it

Thus far we have spoken of the quantity of blood passing through the heart and the lungs in the centre of the body, and in like manner from the arteries1 into the veins2 in the peripheral4 parts and the body at large. We have yet to explain, however, in what manner the blood finds its way back to the heart from the extremities5 by the veins, and how and in what way these are the only vessels6 that convey the blood from the external to the central parts; which done, I conceive that the three fundamental propositions laid down for the circulation of the blood will be so plain, so well established, so obviously true, that they may claim general credence8. Now the remaining position will be made sufficiently9 clear from the valves which are found in the cavities of the veins themselves, from the uses of these, and from experiments cognisable by the senses.

The celebrated10 Hieronymus Fabricius of Aquapendente, a most skilful11 anatomist, and venerable old man, or, as the learned Riolan will have it, Jacobus Silvius, first gave representations of the valves in the veins, which consist of raised or loose portions of the inner membranes12 of these vessels, of extreme delicacy13, and a sigmoid or semilunar shape. They are situated14 at different distances from one another, and diversely in different individuals; they are connate at the sides of the veins; they are directed upwards15 towards the trunks of the veins; the two — for there are for the most part two together — regard each other, mutually touch, and are so ready to come into contact by their edges, that if anything attempts to pass from the trunks into the branches of the veins, or from the greater vessels into the less, they completely prevent it; they are farther so arranged, that the horns of those that succeed are opposite the middle of the convexity of those that and so on alternately.

The discoverer of these valves did not rightly understand their use, nor have succeeding anatomists added anything to our knowledge: for their office is by no means explained when we are told that it is to hinder the blood, by its weight, from all flowing into inferior parts; for the edges of the valves in the jugular16 veins hang downwards17, and are so contrived18 that they prevent the blood from rising upwards; the valves, in a word, do not invariably look upwards, but always toward the trunks of the veins, invariably towards the seat of the heart. I, and indeed others, have sometimes found valves in the emulgent veins, and in those of the mesentery, the edges of which were directed towards the vena cava and vena portae. Let it be added that there are no valves in the arteries, and that dogs, oxen, etc., have invariably valves at the divisions of their crural veins, in the veins that meet towards the top of the os sacrum, and in those branches which come from the haunches, in which no such effect of gravity from the erect19 position was to be apprehended20. Neither are there valves in the jugular veins for the purpose of guarding against apoplexy, as some have said; because in sleep the head is more apt to be influenced by the contents of the carotid arteries. Neither are the valves present, in order that the blood may be retained in the divarications or smaller trunks and minuter branches, and not be suffered to flow entirely21 into the more open and capacious channels; for they occur where there are no divarications; although it must be owned that they are most frequent at the points where branches join. Neither do they exist for the purpose of rendering22 the current of blood more slow from the centre of the body; for it seems likely that the blood would be disposed to flow with sufficient slowness of its own accord, as it would have to pass from larger into continually smaller vessels, being separated from the mass and fountain head, and attaining23 from warmer into colder places.

But the valves are solely24 made and instituted lest the blood should pass from the greater into the lesser25 veins, and either rupture26 them or cause them to become varicose; lest, instead of advancing from the extreme to the central parts of the body, the blood should rather proceed along the veins from the centre to the extremities; but the delicate valves, while they readily open in the right direction, entirely prevent all such contrary motion, being so situated and arranged, that if anything escapes, or is less perfectly27 obstructed28 by the cornua of the one above, the fluid passing, as it were, by the chinks between the cornua, it is immediately received on the convexity of the one beneath, which is placed transversely with reference to the former, and so is effectually hindered from getting any farther.

And this I have frequently experienced in my dissections of the veins: if I attempted to pass a probe from the trunk of the veins into one of the smaller branches, whatever care I took I found it impossible to introduce it far any way, by reason of the valves; whilst, on the contrary, it was most easy to push it along in the opposite direction, from without inwards, or from the branches towards the trunks and roots. In many places two valves are so placed and fitted, that when raised they come exactly together in the middle of the vein3, and are there united by the contact of their margins29; and so accurate is the adaptation, that neither by the eye nor by any other means of examination, can the slightest chink along the line of contact be perceived. But if the probe be now introduced from the extreme towards the more central parts, the valves, like the floodgates of a river, give way, and are most readily pushed aside. The effect of this arrangement plainly is to prevent all motion of the blood from the heart and vena cava, whether it be upwards towards the head, or downwards towards the feet, or to either side towards the arms, not a drop can pass; all motion of the blood, beginning; in the larger and tending towards the smaller veins, is opposed and resisted by them; whilst the motion that proceeds from the lesser to end in the larger branches is favoured, or, at all events, a free and open passage is left for it.

figures 1-2

But that this truth may be made the more apparent, let an arm be tied up above the elbow as if for phlebotomy (A, A, fig30. 1). At intervals31 in the course of the veins, especially in labouring people and those whose veins are large, certain knots or elevations32 (B, C, D, E, F) will be perceived, and this not only at the places where a branch is received (E, F), but also where none enters (C, D): these knots or risings are all formed by valves, which thus show themselves externally. And now if you press the blood from the space above one of the valves, from H to O, (fig. 2,) and keep the point of a finger upon the vein inferiorly, you will see no influx33 of blood from above; the portion of the vein between the point of the finger and the valve O will be obliterated34; yet will the vessel7 continue sufficiently distended35 above the valve (O, G). The blood being thus pressed out and the vein emptied, if you now apply a finger of the other hand upon the distended part of the vein above the valve O, (fig. 3,) and press downwards, you will find that you cannot force the blood through or beyond the valve; but the greater effort you use, you will only see the portion of vein that is between the finger and the valve become more distended, that portion of the vein which is below the valve remaining all the while empty (H, O, fig. 3).

It would therefore appear that the function of the valves in the veins is the same as that of the three sigmoid valves which we find at the commencement of the aorta36 and pulmonary artery37, viz., to prevent all reflux of the blood that is passing over them.

figures 3-4

Farther, the arm being bound as before, and the veins looking full and distended, if you press at one part in the course of a vein with the point of a finger (L, fig. 4), and then with another finger streak38 the blood upwards beyond the next valve (N), you will perceive that this portion of the vein continues empty (L, N), and that the blood cannot retrograde, precisely39 as we have already seen the case to be in fig. 2; but the finger first applied40 (H, fig. 2, L, fig. 4), being removed, immediately the vein is filled from below, and the arm becomes as it appears at D C, fig. 1. That the blood in the veins therefore proceeds from inferior or more remote parts, and towards the heart, moving in these vessels in this and not in the contrary direction, appears most obviously. And although in some places the valves, by not acting41 with such perfect accuracy, or where there is but a single valve, do not seem totally to prevent the passage of the blood from the centre, still the greater number of them plainly do so; and then, where things appear contrived more negligently42, this is compensated43 either by the more frequent occurrence or more perfect action of the succeeding valves, or in some other way: the veins in short, as they are the free and open conduits of the blood returning TO the heart, so are they effectually prevented from serving as its channels of distribution FROM the heart.

But this other circumstance has to be noted44: The arm being bound, and the veins made turgid, and the valves prominent, as before, apply the thumb or finger over a vein in the situation of one of the valves in such a way as to compress it, and prevent any blood from passing upwards from the hand; then, with a finger of the other hand, streak the blood in the vein upwards till it has passed the next valve above (N, fig. 4), the vessel now remains45 empty; but the finger at L being removed for an instant, the vein is immediately filled from below; apply the finger again, and having in the same manner streaked46 the blood upwards, again remove the finger below, and again the vessel becomes distended as before; and this repeat, say a thousand times, in a short space of time. And now compute47 the quantity of blood which you have thus pressed up beyond the valve, and then multiplying the assumed quantity by one thousand, you will find that so much blood has passed through a certain portion of the vessel; and I do now believe that you will find yourself convinced of the circulation of the blood, and of its rapid motion. But if in this experiment you say that a violence is done to nature, I do not doubt but that, if you proceed in the same way, only taking as great a length of vein as possible, and merely remark with what rapidity the blood flows upwards, and fills the vessel from below, you will come to the same conclusion.

点击收听单词发音收听单词发音  

1 arteries 821b60db0d5e4edc87fdf5fc263ba3f5     
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》
2 veins 65827206226d9e2d78ea2bfe697c6329     
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》
3 vein fi9w0     
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。
4 peripheral t3Oz5     
adj.周边的,外围的
参考例句:
  • We dealt with the peripheral aspects of a cost reduction program.我们谈到了降低成本计划的一些外围问题。
  • The hotel provides the clerk the service and the peripheral traveling consultation.旅舍提供票务服务和周边旅游咨询。
5 extremities AtOzAr     
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
6 vessels fc9307c2593b522954eadb3ee6c57480     
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》
7 vessel 4L1zi     
n.船舶;容器,器皿;管,导管,血管
参考例句:
  • The vessel is fully loaded with cargo for Shanghai.这艘船满载货物驶往上海。
  • You should put the water into a vessel.你应该把水装入容器中。
8 credence Hayy3     
n.信用,祭器台,供桌,凭证
参考例句:
  • Don't give credence to all the gossip you hear.不要相信你听到的闲话。
  • Police attach credence to the report of an unnamed bystander.警方认为一位不知姓名的目击者的报告很有用。
9 sufficiently 0htzMB     
adv.足够地,充分地
参考例句:
  • It turned out he had not insured the house sufficiently.原来他没有给房屋投足保险。
  • The new policy was sufficiently elastic to accommodate both views.新政策充分灵活地适用两种观点。
10 celebrated iwLzpz     
adj.有名的,声誉卓著的
参考例句:
  • He was soon one of the most celebrated young painters in England.不久他就成了英格兰最负盛名的年轻画家之一。
  • The celebrated violinist was mobbed by the audience.观众团团围住了这位著名的小提琴演奏家。
11 skilful 8i2zDY     
(=skillful)adj.灵巧的,熟练的
参考例句:
  • The more you practise,the more skilful you'll become.练习的次数越多,熟练的程度越高。
  • He's not very skilful with his chopsticks.他用筷子不大熟练。
12 membranes 93ec26b8b1eb155ef0aeaa845da95972     
n.(动物或植物体内的)薄膜( membrane的名词复数 );隔膜;(可起防水、防风等作用的)膜状物
参考例句:
  • The waste material is placed in cells with permeable membranes. 废液置于有渗透膜的槽中。 来自辞典例句
  • The sarcoplasmic reticulum is a system of intracellular membranes. 肌浆网属于细胞内膜系统。 来自辞典例句
13 delicacy mxuxS     
n.精致,细微,微妙,精良;美味,佳肴
参考例句:
  • We admired the delicacy of the craftsmanship.我们佩服工艺师精巧的手艺。
  • He sensed the delicacy of the situation.他感觉到了形势的微妙。
14 situated JiYzBH     
adj.坐落在...的,处于某种境地的
参考例句:
  • The village is situated at the margin of a forest.村子位于森林的边缘。
  • She is awkwardly situated.她的处境困难。
15 upwards lj5wR     
adv.向上,在更高处...以上
参考例句:
  • The trend of prices is still upwards.物价的趋向是仍在上涨。
  • The smoke rose straight upwards.烟一直向上升。
16 jugular oaLzM     
n.颈静脉
参考例句:
  • He always goes for the jugular.他总是直奔要害而去。
  • Bilateral internal jugular vein stenting is also a rare procedure.两侧内颈静脉支架置放术也是少见的技术。
17 downwards MsDxU     
adj./adv.向下的(地),下行的(地)
参考例句:
  • He lay face downwards on his bed.他脸向下伏在床上。
  • As the river flows downwards,it widens.这条河愈到下游愈宽。
18 contrived ivBzmO     
adj.不自然的,做作的;虚构的
参考例句:
  • There was nothing contrived or calculated about what he said.他说的话里没有任何蓄意捏造的成分。
  • The plot seems contrived.情节看起来不真实。
19 erect 4iLzm     
n./v.树立,建立,使竖立;adj.直立的,垂直的
参考例句:
  • She held her head erect and her back straight.她昂着头,把背挺得笔直。
  • Soldiers are trained to stand erect.士兵们训练站得笔直。
20 apprehended a58714d8af72af24c9ef953885c38a66     
逮捕,拘押( apprehend的过去式和过去分词 ); 理解
参考例句:
  • She apprehended the complicated law very quickly. 她很快理解了复杂的法律。
  • The police apprehended the criminal. 警察逮捕了罪犯。
21 entirely entirely     
ad.全部地,完整地;完全地,彻底地
参考例句:
  • The fire was entirely caused by their neglect of duty. 那场火灾完全是由于他们失职而引起的。
  • His life was entirely given up to the educational work. 他的一生统统献给了教育工作。
22 rendering oV5xD     
n.表现,描写
参考例句:
  • She gave a splendid rendering of Beethoven's piano sonata.她精彩地演奏了贝多芬的钢琴奏鸣曲。
  • His narrative is a super rendering of dialect speech and idiom.他的叙述是方言和土语最成功的运用。
23 attaining da8a99bbb342bc514279651bdbe731cc     
(通常经过努力)实现( attain的现在分词 ); 达到; 获得; 达到(某年龄、水平、状况)
参考例句:
  • Jim is halfway to attaining his pilot's licence. 吉姆就快要拿到飞行员执照了。
  • By that time she was attaining to fifty. 那时她已快到五十岁了。
24 solely FwGwe     
adv.仅仅,唯一地
参考例句:
  • Success should not be measured solely by educational achievement.成功与否不应只用学业成绩来衡量。
  • The town depends almost solely on the tourist trade.这座城市几乎完全靠旅游业维持。
25 lesser UpxzJL     
adj.次要的,较小的;adv.较小地,较少地
参考例句:
  • Kept some of the lesser players out.不让那些次要的球员参加联赛。
  • She has also been affected,but to a lesser degree.她也受到波及,但程度较轻。
26 rupture qsyyc     
n.破裂;(关系的)决裂;v.(使)破裂
参考例句:
  • I can rupture a rule for a friend.我可以为朋友破一次例。
  • The rupture of a blood vessel usually cause the mark of a bruise.血管的突然破裂往往会造成外伤的痕迹。
27 perfectly 8Mzxb     
adv.完美地,无可非议地,彻底地
参考例句:
  • The witnesses were each perfectly certain of what they said.证人们个个对自己所说的话十分肯定。
  • Everything that we're doing is all perfectly above board.我们做的每件事情都是光明正大的。
28 obstructed 5b709055bfd182f94d70e3e16debb3a4     
阻塞( obstruct的过去式和过去分词 ); 堵塞; 阻碍; 阻止
参考例句:
  • Tall trees obstructed his view of the road. 有大树挡着,他看不到道路。
  • The Irish and Bristol Channels were closed or grievously obstructed. 爱尔兰海峡和布里斯托尔海峡或遭受封锁,或受到了严重阻碍。
29 margins 18cef75be8bf936fbf6be827537c8585     
边( margin的名词复数 ); 利润; 页边空白; 差数
参考例句:
  • They have always had to make do with relatively small profit margins. 他们不得不经常设法应付较少的利润额。
  • To create more space between the navigation items, add left and right margins to the links. 在每个项目间留更多的空隙,加左或者右的margins来定义链接。
30 fig L74yI     
n.无花果(树)
参考例句:
  • The doctor finished the fig he had been eating and selected another.这位医生吃完了嘴里的无花果,又挑了一个。
  • You can't find a person who doesn't know fig in the United States.你找不到任何一个在美国的人不知道无花果的。
31 intervals f46c9d8b430e8c86dea610ec56b7cbef     
n.[军事]间隔( interval的名词复数 );间隔时间;[数学]区间;(戏剧、电影或音乐会的)幕间休息
参考例句:
  • The forecast said there would be sunny intervals and showers. 预报间晴,有阵雨。
  • Meetings take place at fortnightly intervals. 每两周开一次会。
32 elevations cb4bbe1b6e824c996fd92d711884a9f2     
(水平或数量)提高( elevation的名词复数 ); 高地; 海拔; 提升
参考例句:
  • Weight of the crust changes as elevations are eroded and materials are deposited elsewhere. 当高地受到侵蚀,物质沉积到别的地方时,地壳的重量就改变。
  • All deck elevations are on the top of structural beams. 所有甲板标高线均指结构梁顶线。
33 influx c7lxL     
n.流入,注入
参考例句:
  • The country simply cannot absorb this influx of refugees.这个国家实在不能接纳这么多涌入的难民。
  • Textile workers favoured protection because they feared an influx of cheap cloth.纺织工人拥护贸易保护措施,因为他们担心涌入廉价纺织品。
34 obliterated 5b21c854b61847047948152f774a0c94     
v.除去( obliterate的过去式和过去分词 );涂去;擦掉;彻底破坏或毁灭
参考例句:
  • The building was completely obliterated by the bomb. 炸弹把那座建筑物彻底摧毁了。
  • He began to drink, drank himself to intoxication, till he slept obliterated. 他一直喝,喝到他快要迷糊地睡着了。 来自《简明英汉词典》
35 distended 86751ec15efd4512b97d34ce479b1fa7     
v.(使)膨胀,肿胀( distend的过去式和过去分词 )
参考例句:
  • starving children with huge distended bellies 鼓着浮肿肚子的挨饿儿童
  • The balloon was distended. 气球已膨胀。 来自《现代英汉综合大词典》
36 aorta 5w8zV     
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。
37 artery 5ekyE     
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。
38 streak UGgzL     
n.条理,斑纹,倾向,少许,痕迹;v.加条纹,变成条纹,奔驰,快速移动
参考例句:
  • The Indians used to streak their faces with paint.印第安人过去常用颜料在脸上涂条纹。
  • Why did you streak the tree?你为什么在树上刻条纹?
39 precisely zlWzUb     
adv.恰好,正好,精确地,细致地
参考例句:
  • It's precisely that sort of slick sales-talk that I mistrust.我不相信的正是那种油腔滑调的推销宣传。
  • The man adjusted very precisely.那个人调得很准。
40 applied Tz2zXA     
adj.应用的;v.应用,适用
参考例句:
  • She plans to take a course in applied linguistics.她打算学习应用语言学课程。
  • This cream is best applied to the face at night.这种乳霜最好晚上擦脸用。
41 acting czRzoc     
n.演戏,行为,假装;adj.代理的,临时的,演出用的
参考例句:
  • Ignore her,she's just acting.别理她,她只是假装的。
  • During the seventies,her acting career was in eclipse.在七十年代,她的表演生涯黯然失色。
42 negligently 0358f2a07277b3ca1e42472707f7edb4     
参考例句:
  • Losses caused intentionally or negligently by the lessee shall be borne by the lessee. 如因承租人的故意或过失造成损失的,由承租人负担。 来自经济法规部分
  • Did the other person act negligently? 他人的行为是否有过失? 来自口语例句
43 compensated 0b0382816fac7dbf94df37906582be8f     
补偿,报酬( compensate的过去式和过去分词 ); 给(某人)赔偿(或赔款)
参考例句:
  • The marvelous acting compensated for the play's weak script. 本剧的精彩表演弥补了剧本的不足。
  • I compensated his loss with money. 我赔偿他经济损失。
44 noted 5n4zXc     
adj.著名的,知名的
参考例句:
  • The local hotel is noted for its good table.当地的那家酒店以餐食精美而著称。
  • Jim is noted for arriving late for work.吉姆上班迟到出了名。
45 remains 1kMzTy     
n.剩余物,残留物;遗体,遗迹
参考例句:
  • He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
  • The remains of the meal were fed to the dog.残羹剩饭喂狗了。
46 streaked d67e6c987d5339547c7938f1950b8295     
adj.有条斑纹的,不安的v.快速移动( streak的过去式和过去分词 );使布满条纹
参考例句:
  • The children streaked off as fast as they could. 孩子们拔脚飞跑 来自《现代英汉综合大词典》
  • His face was pale and streaked with dirt. 他脸色苍白,脸上有一道道的污痕。 来自辞典例句
47 compute 7XMyQ     
v./n.计算,估计
参考例句:
  • I compute my losses at 500 dollars.我估计我的损失有五百元。
  • The losses caused by the floods were beyond compute.洪水造成的损失难以估量。


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