Laet. of Soda, with ani- 3. Globules. M. M. Prevôst and Dumas Dr. Hodgkin 4.1 0.9 Phos. of Lime, with traces 6.0 4000 3200 4076 3000 Pure Lime 20.0 100.0 Carbon. Acid and Loss Dr. Lardner In a systematic account of this subject, we should consider the structure of the heart and blood-vessels, and the powers by which they are enabled to receive and propel the blood. In order to observe these globules, which, Dr. 16.5 Southwood Smith states, are placed in rows, one 100.0 body being beneath the other like a pile of similar When the blood circulates in the vessels, the par- coins when gently thrown down, it is necessary ticles which it contains have no other motion than that the blood, freshly drawn, be slightly and thinly that which is impressed on them by the liquid; but smeared over the surface of a slip of glass, and the moment one is opened they become agitated in a afterwards covered by another plate, so that some lively manner, and the little drop then presents a slight inequalities in the thickness of the layer peculiar species of ebullition, ceasing at the end of a of blood between them will be produced, and which few seconds. Sir E. Home entertained a peculiar are necessary to succeed in causing the very curious opinion on this subject; he supposed that the blood appearances already mentioned. Highly magnifying contains globules (vide cut f), which, in the sound powers are absolutely necessary to be employed in state, are contained within a layer of colouring matthis investigation. ter, as in a shell; at the expiration of thirty seconds from the date of its escape from the blood-vessel, this external matter contracts and forms a kind of collar or ring around the central globule. M. M. Prevost and Dumas differ essentially from Sir Everard on this point; they consider as the usual state that which he views as the effect of death. Their proofs seem irrefragable, since they rest upon observations on the circulating fluid in the wing of the bat, the foot of the frog, the mesentery of fishes, the tail of the miller's thumb (gobius niger, &c.), and the lung of the salamander. They have ascertained, by numerous observations, that the appearance and diameter of the globules were the same within as without the vessels. They perceived that they were not endowed with a rotatory motion upon their centre, as some authors had thought, but that they simply followed the direction of the blood. There cular The arteries receive the blood from the heart, and distribute it to all parts of the body. These vessels are in general less capacious than the veins, but of a more solid texture and more compact; they are highly elastic, and possessed of considerable muspowers. All the arteries of the body are derived from one of two trunks: 1st. The pulmonary artery, which ramifies through the lungs, and the aorta, which, commencing from the left ventricle, is distributed over the whole body. The arteries, after their various ramifications and anastomoses, terminate by communicating with the origin of the veins; so that the blood returns towards the heart in a continuous canal, in which there are no obvious marks of distinction to define the limits between the two orders of vessels. The structure of the veins soon becomes clearly distinguished from that of the arteries; they possess no muscularity; they are much more capacious; less constant in their course and divisions; weaker in their texture; and less elastic than the latter vessels. They are also generally characterized by the possession of valves, to propel the blood towards may be perceived with great facility in the web of the extremities. There are seven large venous trunks a frog's foot, and the tail of the gobius, the different opening into the two auricles of the heart. The vena phases of the globules, and it is easy thus to ascer-cava thoracica and the vena cava abdominalis return tain their flattened form. Sometimes they are seen in plano, sometimes more or less oblique, occasionally only their damp edge appears. Sometimes they are balanced in the equilibrium of the fluid carrying them, at other periods they are seen gently to turn themselves, allowing their form to be observed with greater accuracy. Mr. Hewson thought they possessed elasticity, and M. M. Prevôst and Dumas assure us that each globule is enclosed in a mem-section of an artery and vein, in order to exhibit the branous sac. The following table exhibits the microscopic measurements of these globules, according to the results of different physiologists: the blood from the upper and lower parts of the body to the right, or anterior, or cavic auricle: the coronary vein pours into the same cavity that which had circulated through the substance of the heart itself. The two right and two left pulmonary veins discharge into the left, or posterior, or pulmonic auricle, the blood which has passed through the lungs. In Plate I. fig. 1 is a diagram representing a vertical valves in the latter, by means of which the blood is compelled to ascend in a direction contrary to its own gravity. The arrows show the course of the blood to and from the heart. The heart is placed in the centre of the san- of the body and the ligature, and empty in the rest guiferous system, and is endowed with immense mus- of its course; thirdly, by opening a vein, when cular power, by which it is enabled to distribute and tied, above and below the ligature; fourthly, by circulate the blood through the two orders of vessels microscopical observation in the lower animals. which we have now described. The trunks of the circulating tubes meet together in this part, which is the first mover of the whole animal frame, and sustains, by a perpetual and truly wonderful power, this primary vital function, from the second or third week after conception to the last period of our existence. The passage of the blood from the arteries into the veins seems to follow as a corollary from what we have stated concerning the proofs of its course in these two systems of vessels. We have shown that the ultimate arteries are continuous with the origins of the veins; that the blood moves from the heart to the extremities in the former vessels; that it passes from the extremities to the heart in the latter. The intermediate passage is a direct consequence of these facts. But it may be demonstrated by incontestable proofs independent of this argument. If we tie the artery of a part, its corresponding vein receives no blood; but, if we take off the ligature, the vein is again filled. The quantity of blood expelled from the aortic ventricle is so considerable that the supply can be kept up only by a return of blood to the heart. It is calculated in the human subject that two ounces of blood are expelled at each pulsation; if we suppose eighty pulsations a minute, This organ alternately receives and propels the blood. That which has circulated through the body enters the right auricle by the two vena cava; the coronary vein pours into the same cavity the blood which has supplied the heart itself. The cavic or right auricle propels this, which is venous blood, through the annulus venosus into the right or pulmonic ventricle, and it goes from this cavity to circulate through the lungs by the pulmonary artery. It is again brought back to the heart by the four pulmonary veins into the left or pulmonic auricle. It becomes changed from the state of venous to that of arterial blood, which takes place during its circu-9600 ounces will be thrown into the aorta in an lation through the lungs. From the left auricle it passes through the left annulus venosus into the aortic ventricle of the same side, and is thence expelled by the aorta into the arterial system of the whole body. From the minute arteries it enters the origins of the venous system, and is again poured into the heart by three venous trunks which we have already mentioned. This passage of the blood through the cavities of the heart is regulated and maintained in an undisturbed succession by valves placed at the different openings, which prevent all reflux of the circulating fluid. hour, and 4400lbs. in a day. The same blood therefore which the aorta received from the heart must return to this viscus, and the only passage by which it can return is by the veins. Nearly the whole blood of the body will be discharged from the wound of any large blood-vessel. Lastly, the passage of the blood from the arteries into the veins may be proved by ocular demonstration in living animals. The use of the microscope affords this proof in the transparent parts of cold-blooded animals, as the mesentery and web of the foot in frogs, the tail of fishes, &c. The motions of any part of the heart, considered singly and individually, consist in a constant series of alternate contractions and dilatations, or, as they are technically termed, alternate states of systole and Having thus described the course and peculiarities of the blood, we think it proper to subjoin the proofs and experiments on which it is supported, although the fact of the circulation has been so long admitted, and is now so generally established, that the enume-diastole. The contractions take place as in other ration may to some persons appear superfluous. The course of the blood through the heart, i. e. from the cavic auricle to the aortic ventricle, by means of the lungs, is manifest from the structure of the heart itself. The valves, which are placed at its various apertures actually will not admit of the blood's motion in any other direction than what we have described. muscles; the dilating cause consists in the forcible entrance of the blood into the cavity. The auricles and ventricles, when viewed in relation to each other, are successively contracted and dilated; the corresponding parts acting at the same time on both sides of the heart. Thus, when the auricles contract, in order to expel the blood which they have received from the system at large and from the lungs, the That the blood passes from the heart into the ventricles are relaxed, and therefore are in a fit state trunk of the aorta, thence into its branches, and so for receiving this blood. When, in the following on to the most minute ramifications, is evinced, moment, the recently-filled ventricles contract, in first, by the effect of ligatures on these vessels: the order to urge the blood forwards into the two arterial artery becomes turgid between the heart and the trunks, the auricles are relaxed, and become immeligature, and empty between the ligature and its dis-diately distended with the current of venous blood. tribution; secondly, by opening an artery, when tied, above and below the ligature; the blood in this case flows only from the opening which is nearest to the heart; thirdly, by ocular testimony; the passage of the blood can be seen with the aid of magnifying glasses in frogs, fishes, &c., &c. The passage of the blood through the veins, in a contrary course to that in which it flows along the arteries, i. e. from the minute ramifications towards the trunks, and thence to the heart, is proved, first, by the structure and disposition of the valves, which afford an invincible impediment to all retrograde motion; secondly, by ligatures on these vessels, which make the vein turgid between the extremities The action of the heart, and of the vessels connected with it, may therefore be distributed into successive periods. In the first of these, the venæ cave and pulmonary veins pour their blood into the two auricles, and thus cause a diastole of these cavities. The systole of the auricles transmits the blood into the ventricles in the second period; and these latter cavities expel their contents into the arteries in the third portion of time. Thus the action of the veins takes place at the same point of time with that of the ventricles, and the contraction of the auricles is synchronous with that of the arteries. The systole of the ventricles, which is supposed to. occupy one-third of the time of the whole pulsation Spigelius 4800 3600 The female sex are observed, cæteris paribus, to have a more frequent pulse than the male; and short persons exceed tall ones in this respect. It is also remarked that the inhabitants of cold climates have slow pulses. It is familiarly known that the intercourse, by exercise of the body, and, in the human subject, by affections of the mind. The latter causes indeed, if carried to a considerable extent, produce most vehement palpitations of the heart. In saying this much of the pulse, we have thought it more natural to refer it to the heart, which is its source, than to the arteries, in which it is commonly examined. of the heart, is accomplished by an approximation of the sides of the cavities to the middle partition, and of the apex to the basis of the heart. The whole viscus by this means becomes shortened and more obtuse. The well-known fact of the heart's striking against the left breast in its contraction may seem on the first glance to refute this account of the systole of the ventricles. But, on a further examination, it can have no such effect, since the phenome-pulse is accelerated by taking a meal, by the act of non in question depends on two causes amply sufficient to produce this effect, which have been long ago explained by Ferrein and Senac. The swelling of the auricles which are at the back of the heart, and particularly of the left auricle, which is interposed between the spine and the base of the left ventricle, necessarily causes the point of the heart to advance towards the side; and this motion may be imitated in the dead body by injecting or inflating the auricles. The other cause consists in the connexion of the large arteries, particularly the aorta. The curve of that vessel approaches nearly to a straight line; its posterior end, being firmly attached to the vertebræ, is immovable; to its anterior and movable part is affixed the heart, which by the straightening of the vessels is obliged to describe a portion of a circle, in doing which the apex strikes against the side. These two circumstances occur simultaneously; the venous blood rushes into the auricles at the same time that the contracting of the ventricle fills the aorta. It has been questioned whether the heart expels the whole of the contained blood in its systole. It seems that this is the case in a healthy animal, although it has been denied on the faith of experiments. In these inferences we must be cautious, as they are drawn from the interrupted and disordered action of the heart of an animal expiring, under the torture of an experiment, to the living functions of the viscus. If any blood remains in the ventricle, it excites a constant contraction of the cavity. In some cold-blooded animals, and in the incubated chick, the heart is observed to become completely pale in its systole, which proves an entire evacuation of the ventricles. The impulse of the blood expelled by the systole The pulsations of the heart proceed in a regular of the aortic ventricle is felt in the whole arterial and continued succession to the last period of life, system; and it produces in all arteries which come and then all its parts do not cease to act at once; within the sphere of the touch, and which have an but the right auricle and ventricle survive the area of not less than one-sixth of a line in dia- opposite cavities for some little time, so that the meter, an obvious and perceptible effect, called the former fact has been called the ultimum moriens. The pulse, which is a real state of diastole of the artery, blood which returns by the venæ cavæ, after the last and which is synchronous with the systole of the expiration, no longer finds the usual passage through heart. The number of pulsations in a given space of the lungs, which are contracted, but it is still urged time varies infinitely in healthy persons. Age is the on from behind by that which the aorta has rechief cause of these varieties; but other circum-cently propelled. Hence it is forced into the right stances, which constitute the peculiar state of each auricle, and excites contraction in that part by the individual, have considerable effect; so that no stimulus of its presence, some time after the left side standard can be settled which shall prove generally has been at rest. This congestion on the right correct. The following numbers afford, we believe, as side in the last agony explains the empty state of near an approximation as can be expected amidst so the arteries, particularly the larger ones after death. much uncertainty; they will serve at least as a com- Sabatier has ascribed to the same cause the greater parative view in subjects of different ages. relative capacity of the right ventricle and auThe heart of an infant, sleeping tranquilly, per-ricle of the adult heart. The appearance which we forms, according to Dr. Heberden, in the first days of its existence about 140 pulsations in a minute. At the end of the first year second year third and following year At the age of manhood sixtieth year 124 65 are now alluding to does not admit of explanation from any circumstance connected with the healthy functions of the heart and lungs; yet Saba110 tier's statement can hardly be received as completely 96 satisfactory. For, not to mention that we seldom 86 find these cavities actually distended, this explana80 tion supposes the veins to pour their blood into the 75 heart with greater force than the ventricle can exert in reacting, which does not appear probable from comparing the structure of the two parts. The facts, however, contained in the memoir above mentioned, deserve attention. It is stated that by opening the venæ cavæ, and tying the aorta, which prevents accumulation of blood on the right and causes it on the left side of the heart, the left cavities will be found after death to exceed the capacity of the right. This experiment would have been more convincing had the difference been ascertained with certainty and correctness, instead of resting on the inaccurate ground of a mere inspection. beyond which time the variations are very great. Harvey} Riolan Regius Cardanus Bartholine Plempius 2000 3000 4000 4400 |