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Philadelphia. The idea has been esteemed to be confirmed by the fact of excitants having been seen under the microscope, by Hastings, Wedemeyer, and others, to occasion not only contraction but dilatation of the capillaries. The phenomena observed in the erectile tissues have likewise been considered to favour the hypothesis; but in answer to these arguments it may be replied, that the irregular excitation, produced in the parts by the application of powerful stimulants, might readily give occasion to an appearance of expansibility under the microscope, without our being justified in inferring, that these vessels possess an innate vital property of expansibility; and, in many of the cases, in which ammonia and galvanism were applied by Thomson, Hastings, Wedemeyer, and others, the action of contraction ought rather to be esteemed physical or chemical than vital. The results of the application of such excitants, as diluted alcohol, dilute solutions of ammonia and chloride of sodium, can alone be adduced as evidences of vital action on the part of those vessels. The dilatation of the capillary system and of the smaller arteries, which has been remarked on the contact of those agents, is not, as Oesterreicher1 has remarked, the primary effect: it is the consequence of the afflux of blood to the irritated part, as was demonstrated, also, in the experiments of Kaltenbrunner on inflammation, to which allusion has been made. Lastly, attentive observation of the phenomena presented by the erectile tissues must lead to the conclusion, that turgescence of vessels is not the first link in the chain of phenomena; excitation is first induced in the nerves of the part-generally through the influence of the brain, and thence, perhaps, through the sympathetic nerve,-and the afflux of fluid supervenes on this. The vital expansibility of the capillaries cannot, we think, be regarded as proved, or probable.

Professor Draper, of New York, maintains, that the great agency in the circulation of the blood is of a physical character; and is dependent upon the chemical relations of that fluid to the tissues with which it is brought in contact. On the principles of capillary attraction-he says -a liquid will readily flow through a porous body for which it has a chemical affinity; but it will refuse to flow through it, if it has no affinity for it. On this principle he explains why the arterial blood presses the venous before it in the systemic circulation, and why the reverse takes place in the pulmonic. "The systemic circulation takes place because arterial blood has a high affinity for the tissues, and venous blood little or none. The pulmonary circulation takes place because venous blood has a high affinity for atmospheric oxygen, which it finds on the air cells of the lungs; and arterial blood little or none. On the same principle we may explain the rise of sap in trees, the circulatory movements in the different animal tribes, and the minor circulations of the human system."2 Dr. Dowler, of New Orleans, whilst he earnestly combats the views of Professor Draper, is a strong

3

1 Versuch einer Darstellung der Lebre vom Kreislauf des Blutes, Nürnberg, 1826.

2 A Text-Book of Chemistry, p. 392, New York, 1846; and On the Forces which Produce the Organization of Plants, chap. iii.

3 Researches, Critical and Experimental, on the Capillary Circulation. (Reprinted from the New Orleans Medical and Surgical Journal.) January, 1849.

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162

advocate for the distinct action of the capillary vessels, and he adduces a number of striking experiments to establish his position. In perhaps one-fourth of the dissections which he records, the bodies were carried to the dissecting-room a few minutes after death. The external veins, chiefly those of the arms and neck, sometimes became distended; and when they were opened, the blood often flowed in a good stream, and was, at times, projected to the distance of a foot or more. In some cases, by putting a ligature around the arm, or by grasping it above the elbow, the blood was made to flow more freely, and by moving the muscles, as is done in ordinary bloodletting, the blood shot forth for some distance. Punctures in the middle of the subclavian discharged blood, which arose in a full stream, against gravity, two or three inches; sometimes forming an arch as it fell. The coronary veins discharged blood rapidly and "with surprising force." The dissections are considered by Dr. Dowler to show conclusively the independent action of the capillaries; "which in yellow fever, and other acute fevers, probably survives respiration and the heart's action; and when it ceases cadaveric hyperæmia takes place." Such is doubtless the fact; but it may still be questioned, whether anything more than the physical capillarity invoked by Professor Draper is concerned in the phenomenon. In a case observed by the author, and referred to elsewhere, blood

Fig. 299.

b

b

flowed freely from the vessels of the brain, and coagulated fifteen hours after the cessation of respiration and circulation; and many similar cases are on record.

The circulation through the capillaries has long been an interesting topic of microscopic research. According to Wagner, a magnifying power of from two to three hundred diameters is required to make out the particular details. The blood in mass, or in the larger channels, he says, is seen to flow more rapidly than in the smaller. Here the blood corpuscles advance with great rapidity, especially in the arteries, and with a whirling motion, and form a closely crowded stream in the middle of the vessel, without ever touching its parietes. With a little attention, a narrower and clearer, but always very distinct space is seen to remain between the great middle current of blood corpuscles and the walls of the vessel, in which a few white corpuscles, or what Wagner considers to be lymph corpuscles, are moved onwards, but at a much slower rate. These white corpuscles swim in smaller numbers in the transparent liquor sanguinis,

a

Small Venous Branch, from the Web of
Frog's Foot, magnified 350 diameters.

b, b. Cells of pavement epithelium, contain

a

ing nuclei. In the space between the current vessel, the round transparent lymph globules

of oval blood corpuscles, and the walls of the

(?) are seen. (Wagner.)

1 Elements of Physiology, translated by R. Willis, § 122, Lond., 1842.

Fig. 300.

and glide slowly, and in general smoothly, though they sometimes advance by fits and starts more rapidly, but with intervening pauses; and, as a general rule, at least ten or twelve times more slowly than the corpuscles of the central stream. The clear space, filled with liquor sanguinis and white corpuscles, is obvious in all the larger capillaries, whether arterial or venous, but ceases to be apparent in the smaller intermediate vessels which admit but one or two rows of blood corpuscles (Fig. 283). In these vessels, two sets of corpuscles proceed pari passu; but, according to Wagner, it is easy to see, that the blood corpuscles glide more readily onwards, the white corpuscles seeming often to be detained at the bendings of vessels, and at the angles, where anastomosing branches are given off: here they remain adherent for an instant, and then suddenly proceed onwards. These phenomena are observed in every part of the peripheral systemic circulation; but an exception appears to exist in the pulmonic circulation; the capillaries there being filled with both kinds of corpuscles to their very walls.

b

a

It is in this-the intermediate -part of the sanguiferous system, that most important functions take place. In the smallest artery we find arterial blood; and in the smallest vein com- Large Vein of Frog's Foot, magnified 600 diameters. municating with it blood always b, c. Blood corpuscles. a, a. Lymph corpuscles (?) principally conspicuous in the clear space near the possessing venous properties. parietes of the vessel. (Wagner.) Between those points, a change

must have occurred, the reverse of that which happens in the lungs. It is here, too, that nutrition, secretion, and calorification are effected. In the explanation of these functions, we shall find it impossible not to suppose a distinct and elective agency in the tissues concerned; and as it is by such agency, that the varying activity of the different functions is regulated, we are constrained to believe, that the capillary vessels may be able to exert a controlling influence over the quantity and velocity of the blood circulating in them. In disease, the agency of this system of vessels is an object of attentive study with the pathologist. To its influence in inflammation we have already alluded; but it is no less exemplified in the more general diseases of the frame,-as in the cold, hot, and sweating stages of an intermittent. Local, irregular capillary action is, indeed, one of the most common causes or effects of acute diseases, and this generally occurs in some organ at a distance from the seat of the deranging influence. It is a common and just observation, that getting the feet wet, and sitting in a draught of air, are

more certain causes of catarrh than sudden atmospheric vicissitudes, that apply to the whole body; and so extensive is the sympathy between the various portions of this system of vessels, that the most diversified effects are produced in different individuals exposed to the same common cause; one may have inflammatory sore throat; another, ordinary catarrh; another, inflammation of the bowels;-according to the precise predisposition, existing in the individual at the time, to have one structure morbidly affected rather than another;-but these are interesting topics, which belong more strictly to the pathologist.

By the united action, then, of the heart, arteries, and capillary or intermediate system of vessels, the blood attains the veins. We have now to consider the circulation in these vessels.

d. Circulation in the Veins.

It has been already observed, that Harvey considered the force of the heart to be of itself sufficient to return the blood, sent from the left ventricle, to the heart; whilst Bichat conceived the whole propulsory

A

Fig. 301.

effort to be lost in the capillaries, and the transmission of the blood along the veins to be entirely effected by the agency of the capillary system. It is singular, that an individual of such distinguished powers of discrimination should have been led into an error of this magnitude. It is a well-known principle in hydrostatics, that although water, when unconfined, can never rise above its level at any point, and can never move upwards; yet, by being confined in pipes or close channels of any kind, it will rise to the height from which it came. Hence the water or blood in the vessel A, Fig. 301, which may be considered to represent the right auricle, would stand at the same height as that in the vessel B, which we may look upon as the left ventricle,-were they inanimate tubes. We need be at no loss, therefore, in understanding how the blood might attain the right auricle, when the body is erect, by this hydrostatic principle alone; but we have seen, that the force exerted by the heart, arteries, and capillary system is superadded to this, so that the blood would rise much higher than the right auricle, and consequently exert a manifest effort to enter it. It may be remarked, also, that the left ventricle is not the true height of the source, but the top of the arch of the aorta, which is more elevated by several inches than the right auricle. A similar view is embraced by Dr. Billing; but Dr. Carpenter-in commenting on the author's observations on this subject-suggests, that the influence of this hydrostatic

1 First Principles of Medicine, Amer. edit., p. 36, Philad., 1842.

• Human Physiology, § 516, Lond., 1842.

force would scarcely be felt through the plexus of capillary vessels; "for the interposition of a system of tubes even of much larger calibre would be, by the friction created between the fluid and their walls, an effectual obstacle to the rapid ascent of a current, which had so slight an impetus as that derived from its previous fall." The author did not mean, however, to say more than that the blood "might attain" the right auricle by the hydrostatic force alone: he did not wish to convey the idea, that the circulation could be carried on without the aid of an additional force; but that a slight effort only on the part of the heart and arteries might be needed to enable the blood to perform its entire circuit. It is proper to add, that in the last editions of his valuable work, Dr. Carpenter has omitted those comments on the observations of the author.

Are we then to regard the veins as simple elastic tubes? This is the prevalent belief. Their elasticity is, however, much less than that of the arteries. Some physiologists have conceived them to possess contractile properties also. Such is the opinion of M. Broussais, who founds. it, in part, upon certain experiments by M. Sarlandière, already referred to, in which contraction and relaxation of the vena cava of the frog were seen for many minutes after the heart was removed from the body. These pulsations of the venæ cave, and of the pulmonary veins in their natural state, have been seen by numerous observers-by Steno, Lower, Wepfer, Borrachius, Whytt, Haller, Lancisi, Müller, Marshall Hall, Flourens, J. J. Allison, and others. The experiments of Dr. Allison, in reference to the vena cava and pulmonary veins, appeared to him to prove ;-that they pulsate near the heart in the four classes of the vertebrata ;—that in dying animals they pulsate long after the auricle and ventricle have ceased;-that they also beat even in quadrupeds, for hours after they have been separated from the heart and from the body; and that they can be stimulated to contract, either in or out of the body, by mechanical and galvanic agency, especially by the latter, after all motion has ceased for some time.

2

It has been deemed doubtful, whether the veins generally possess any contraction like that of the vena cava and the pulmonary veins near the heart, for although irritated by galvanic and mechanical stimuli by Haller, Nysten, Müller, J. J. Allison, and others, no motion whatever could be detected in them. It has been before shown, however, that nonstriated muscular fibres enter into their composition, and Gerber affirms, that the fibres of their middle coat bear a stronger resemblance to those of muscular tissue than do those of the corresponding coat of the arteries, which more resemble ordinary elastic fibres; but Dr. Carpenter3 thinks it not improbable, that his observations were made on portions of the veins near the heart, which partake of its contractility.

In the experiments of Dr. Marshall Hall on the circulation in the

1 Traité de Physiol., &c., Drs. Bell's and La Roche's translat., p. 391, Philad., 1832. 2 See the experiments of the last named gentleman, proving the existence of a venous pulse independent of the Heart and Nervous System, in Amer. Journal of the Medical Sciences, Feb., 1839, p. 306. 3 Human Physiology, § 514, note, Lond., 1842.

4 Essay on the Circulation, ch. i., Lond., 1831, and Philad., 1835.

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