side, and forms the vena cava descendens, which is immediately joined by the vena azygos. The vena cava descendens carries the blood onwards to the right or pulmonary auricle, where, meeting with that returned by the vena cava ascendens, which is the trunk of the venous system of the lower extremities and the abdomen, and that returned by the coronary vein of the heart, the fleshy parietes (walls or sides) of the auricle are distended, stimulated to action, and contracting, propel the blood through the tricuspid valve into the right or pulmonary ventricle. The mixture of chyle and of absorbed fluids and of the effete and dark blood then enters the pulmonary (or right) ventricle, which being stimulated, contracts and propels the fluid through the pulmonary artery, namely, to the lungs, where the whole receives its ultimate perfection by means of atmospheric influence in the lungs, throwing off its black and carbonaceous matter, and becoming oxygenated and purified, assumes a vermilion or scarlet hue, and then becomes complete and perfect blood, fit for the due continuance of animal heat, and for its exciting and nutritious circulation through the frame. It then has the different parts and qualities presently enumerated, and is thereupon conveyed by the four pulmonary veins into the left auricle of the heart; which being similarly excited by the renovated blood in its own coronary arteries, contracts and propels the blood through the left auriculo ventricular opening into the left ventricle, which also similarly contracting, propels the blood into the aorta. Two branches of this main artery immediately circulate the renovated blood though the coronary arteries, and thus continuously excite the heart itself to action according to the opinion of some authors: and the rest of the branches of the aorta maintaining the like contractile motion, propel the blood into all the arteries and their capillaries, and thence into the veins and over all the system; its renovating particles being nevertheless dispensed and retained in the various parts of the frame through which the general mass of the fluid passes. One portion of this renovated blood flows to the brain, to stimulate the source of the nervous system, the larger portions throughout the arteries of the trunk, and the upper and lower extremities; other portions are dispersed through the peculiarly formed labyrinths of the glands, and in the excretory ducts and the exhaling vessels, forming the various secretions and excretions, whilst the remainder of the blood, impregnated with carbon, and of a dark colour, verging to purple or black, returns by the veins towards the right auricle of the heart. (m) In the veins and other remote parts of the body such blood loses a certain quantity of its original invigorating constituents, and is thus gradually more and more reduced to the state of venous blood, whilst the thoracic duct gradually pours into the great subclavian vein the new materials, arising from digestion and absorption necessary to supply the loss which it has thus experienced in the capillaries and veins; and then the whole of the materials collected as before in such subclavian vein are again and again successively passed into the right auricle and ventricle of the heart, and from thence into and through the lungs in perpetual and unremitting succession as long as life continues.(n) According to this view of the subject, the process of the conversion of venous into arterial blood will consist in the addition of a quantity of carbon, hydrogen, and oxygen, with a proportion of nitrogen. In passing through the lungs a portion of carbon, oxygen, and hydrogen are separated, under the form of carbonic acid and water, merely abstracted from (m) 2 Dungl. Phy. 35 to 58; El. Blum. 377 to 381, tit. Sanguification; 3 Bell, 238, 239; 2 Bost. 479. This summary is principally from Lizars, 141 to 143, who is particularly clear upon the subject; and CHAP. V. OF THE CHAP. V. OF THE 4. Its co lour.(p) 5. Smell, the pulmonary blood by a species of secretion, while in the course of the The blood, when returned from the lungs into the left auricle of the heart and into the aorta, and whilst it continues in the aorta, is in health, a fluid of a rich scarlet or vermilion colour, and is replete with oxygen; but when it has passed into the veins, it becomes carbonized and of a dark purple, and when returned in the veins near to the heart, is almost black.(g) In the veins it has become effete, and, therefore, in cases of plethora, or when the body is incumbered with too much or impure blood, and it becomes expedient to withdraw a portion by bleeding, an operation is usually performed on a vein.(r) Hence, Blumenbach, instead of terming blood in the arteries arterial, and that in the veins venous, (the usual appellation) suggests the expediency of terming the former oxygenized blood, and the latter carbonized blood.(s) The blood, before it has become coagulated, varies in colour according to the part of the frame where it is found. It is vermilion or scarlet coloured in the arteries, because it has but just before been oxygenated; strong purple in the veins, because in passing through the arteries into the same, it has become in a degree carbonized and incumbered with various particles, and almost black, before its intermixture with the materials of the new blood from the thoracic duct; because, in its passage through the capillaries and veins, it has become completely carbonized and incumbered.(t) The exchange of colour from the dark purple or almost black venous blood, to the scarlet arterial blood, takes place in the lungs, and is, it is supposed, occasioned by the oxygen of the arterial blood acting upon the small particles of iron, and thus changing the colour.(u) It has been observed that in surgical operations, after a tourniquet has been applied to an arterial trunk, the blood which first flows, when we remove the instrument, is perceived to be of the venous colour, and it was remarked by Hunter, that extravasated blood is always purple, even in cases where there is every reason to suppose that it may have proceeded from an artery; from whence a conclusion has been drawn that the change from the arterial to the venous state may take place by the action of the constituents of the blood upon each other while it remains in the great trunks in a situation where it is incapable of receiving any addition of extraneous matter.(x) But some of the most distinguished anatomists and physiologists of the present time deny this result. Blood has a peculiar odour; at first, especially when still warm, it emits feel, taste, a vapour, of late denominated an animal gas, and shown to consist of hydrogen and carbon suspended by caloric.(y) &c., of blood. When extracted, blood feels thick and unctuous, is of a slightly saline (0) Bost. 479. (p) See Dr. Turner's Chem. 547. (r) See post, tit. Bleeding; 1 Bell, is incorrect, for it is fresh and arterial (s) El. Blum. 9, note (i.) (u) 2 Bost. 98; 1 Bost. 372; 3 Bost. (y) El. Blum. 7; 1. Bost. 354; 2 Dungl. tuste, rather mucous, and varying in the different parts of the body. In the heart or at the centre of the circulation, it differs from what it is in the glands, excretories, and all the extremities of the body; different in the liver, among the intestines, in the cheeks and lips, in the reservoir or sinuses of the head and womb. (z) CHAP. V. OF THE It seems now to be agreed that one of the principal effects of respira- 6. Heat of tion is the arterialization of the blood by means of the introduction of free the blood and tempeoxygen and the discharge of carbonic acid. (a) But it has been generalrature gely insisted that this occasions combustion and consequent heat in the nerally. (a) lungs.(b) Some authors, however, have insisted, that if oxygen do communicate heat, "it does so, not to the lungs, nor to the blood in the lungs in particular, but to the whole body through the medium of the blood," namely, by the continual passing and action of the blood through all parts of the frame. (c) The heat of the blood at the heart in health is usually from 96 to 100 Fahrenheit's thermometer, but sometimes in diseases it rises to 106.(d) The temperature of the natural atmosphere is generally much lower than that of the blood, but sometimes it exceeds it, and man is capable of living in a temperature exceeding his own.(e) The heat of all parts is ceteris paribus, commensurate with the quantity of blood circulating through them, and our temperature depends upon respiration. (f) It is supposed that at and near the heart the temperature is 100, and the weight of authority seems to establish, that the temperature of the arterial is somewhat, though not much greater, than that of the venous blood; (g) in the large arteries, to a degree or a degree and a half higher than in the corresponding veins. (h) The conclusion which Crawford deduced was, that the specific heat of arterial is greater than that of venous blood in an average proportion of 114.5 to 100, but that the general temperature is nevertheless equalized by a threefold operation, and by the completion of the combination of the oxygen and carbon, in the capillary part of the circulation, and not entirely in the lungs, where they are first in a degree only combined.(i) blood. Certain salts are always found in blood, and which it is said are rather 7. Of the more than 9 grains in 1000 grains of serum; of these 9 grains, about 6 salts in are muriate of soda combined with a small quantity of muriate of potash, and about 1 of the subcarbonate of soda, with minute quantities of the sulphate of potash, and the phosphates of lime, iron, and magnesia. (k) The use of the salt in the blood has been said to be that they stimulate the nerves of the heart, and thus contribute to the contraction of its muscular fibres,() that they aid in the operation of the secreting organs, and contribute to the process of digestion; but others observe that these suppositions are gratuitous.(m) However, there are certainly numerous be (z) 1 Bell, 52, 522; El. Blum. 7. (a) See post, Temperature. (b) 1 Bell, 543; 2 Dungl. Phy. 94 to 106; 2 Bost. 195 to 229, stating the general results of experiments and opinions; and see Respiration, post; and 2 Bost. 192; chap. vii. of Animal Temperature; and Stevens on the Blood. (c) 1 Bell, 545, 547, notes; and Dr. Stevens on Blood, 27. (d) Coop. Dict. tit. Inflammation; El. Blum. 7, 155, 158, says its temperature is about 96 of Fahrenheit; Dr. Good, 98, (see vol ii. 34,) in which latter Dr. Bostock appears to agree, 1 Bost. 348, 349. (e) 2 Dungl. Phy. 170 to 194; 2 Bost. 192, &c. (f) El. Blum. 164, 165, 167. (h) 1 Bost. 387, note. (i) See 2 Bost. 204 to 206. (k) Dr. Marcet, Med. Chir. Trans. vol. ii. p. 370; 1 Bost. 384; Turner's Chem. 548; muriate of soda is the chief saline ingredient in the blood, Dr. Stevens on Blood. 296; large doses of muriate of soda and other active salines should be administered in fever, id. ibid.; salty taste, 2 Horner, Anat. 175. (1) Whytt's Works, p. 26. (m) 1 Bost. 385; Stevens on Blood, 319. CHAP. V. OF THE 8. Animal neficial effects arising from the saline particles in the blood, and they directly tend to prevent putrefaction and assist vitality and the continuance of general health.(n) Some physiologists also insist that Sulphur is one of the constituents of the blood, but others deny its presence.(o) Although the animal substances which enter into the composition of substances. the blood possess properties both chemical and physical which are sufficiently characteristic to distinguish them from each other, yet they may all be resolved into the same ultimate elements, namely, Carbon, Oxygen, Hydrogen, and Azote, also termed Nitrogen. The following is the scale of proportions, according to MM. Gay Lussac and Thenard,(p) but the results of experiments vary. Azote or The following is the latest analysis of healthy blood that has been made in this country, [England,] but the exact proportions vary.(g) The proportions of azote, (from a privative, and on life, because it is nitrogen. unable of itself, to support the respiration of animals,) or nitrogen, to which it is synonymous, it is supposed increases as age advances, and there is more fibrin in the blood of the adult than in that of the infant.(7) 9. Chemical properties. With respect to the chemical properties of fibrin, they appear exactly to resemble those of the muscular fibre. It is acted upon in the same manner by nitric acid and the other re-agents, so as to be fully entitled to the ancient appellation of liquid flesh.(s) 10. Weight As respects the specific gravity of blood in general, when it is in its and quanti- ordinary healthy and mixed state, it may be estimated as 1050, to water ty of blood being 1000.(t) The specific gravity of the serum of arterial blood has in entire human frame. been generally found to be less than that of venous.(u) Hunter, in his celebrated treatise on Blood, states that it appeared to him impossible to ascertain the entire quantity of blood in the body, and that the knowledge of it would probably give but very little assistance towards better understanding the economy of the animal; but that the quantity is probably as permanent a circumstance as any, and not depending on immediate action.(x) It should seem, however, to be desirable to endeavour to ascer (n) Stevens on the Blood, 318. (0) 1 Bost. 385. (p) Stevens on Blood, 3; and 1 Bost. 385. (9) Stevens on Blood, 3 and 4. But see Copland's Dict. tit. Blood. (r) 1 Bost. 386. (s) Id. 349, 350. (t) El. Blum. 7; 2 Good. 34; 2 Dungl. Phy. 40. (u) See 2 Bost. 78, note, fully. (x) Hunter on the Blood, 69. tain the entire quantity of blood to be found in the healthy state, and what subtraction of that fluid can be borne without danger to life,—it is indeed essential as regards the remedies for various diseases by bleeding, to know precisely what will be the effect in the diminution of the states of various diseases, and consequently more precision as regards the knowledge of the usual quantity of blood, would be interesting and most desirable. (y) As respects weight, Dr. Davy's experiments tend to establish that pure fibrin is heavier than serum, but that the mixture of fibrin and serum, which constitutes the buffy coat, is lighter than the mixture of fibrin, serum and red particles, and therefore floats on the surface; and that in inflamed blood the serum and coagulable lymph are less viscid, that is, less glutinous or tenacious than ordinary. The specific gravity of the red particles he found to be 1087. That the formation of the buffy coat does not appear to bear any exact relation to the specific gravity of the blood. In acute disease the blood, whether buffed or not, is generally of greater specific gravity than ordinary; in diseases of debility the reverse.(z) That the formation of the buffy coat is supposed to depend on the viscidity (glutinous or tenacious quality of the blood) as connected with the proportion of water, or the complete mixture of its ingredients, and that heat is not extricated during the coagulation either of fibrin or of serum.(z) With respect to the actual quantity and weight of blood in the entire system, our means of determination are so inexact, and consequently the calculations, or rather the conjectures, that have been offered upon the subject, are so strikingly discrepant, that it is not easy to reach a satisfactory conclusion. It is only necessary to state a few of the different opinions that have been offered, to show the singularity of several. Allen, Muller, and Abildgaard estimate the weight, even in an adult, at very little more than eight pounds, at 12 ounces to the pound; Harvey at 9, Blumenbach, at 10, Borrelli at 20, Planche at 28, Haller at thirty pounds, Lizars the same, Dr. Young at 40, Hamberger at 80, and Keil at 100:(a) Perhaps this discrepancy may have arisen from the latter calculators including other fluids besides proper blood. Of these enumerations it has been observed by Blumenbach, that the former are nearer the truth,(b) and that the proportion to the weight of the body is as 1 to 5; (c) but in another part of that excellent work, it is supposed that the mass of the blood is only 10 pounds of 12 ounces each, or 120 ounces. (d) But this seems contradictory, for few adults weigh less than 150 pounds, and one-fifth of that weight would be 30 pounds. Dr. Good observes, that the mean number, as given by Baron Haller and Dr. Young, making the amount from 30 to 40 lbs., appears most reasonable, and that the same perhaps fall not short of the sum intended by Professor Blumenbach, but that the subject requires farther examination, and a nicer estimate. (e) Lizars observes, that according to the most unexceptionable calculations, the quantity of blood in the body is estimated at thirty pounds, each pound being twelve ounces;(f) and Dr. Bostock seems to consider that thirty-three pounds, of twelve ounces each, may be properly considered as the weight of the whole mass of blood,(g) and that of this about threefourths are constantly in the veins, and one-fourth only in the arteries.(h) Certainly it would be extraordinary, if there be only eight or ten pounds' (y) Dr. Stevens on Blood, 338, mentions an instance of taking forty ounces of blood from the arm at one bleeding, and not unfrequently a much larger quantity has been taken at a time; and an instance recently occurred at one of the public offices, of 120 ounces having been subtracted, and the party survived ten days. (z) Ed. Med. Jour. vol. xxix. page 244; 3 Bost. 322. (a) 2 Good, 20, 21; El. Blum. 7, note (b) El. Blum. 7, note, (e.) (e) 2 Good, 21. (ƒ) Lizars, part ii. page 146. 1 Bost. 388. Id. 288, 388; 1 Haller, El. Phy. 3. CHAP. V. SECT. II. BLOOD. |