3

can exist in it so as to exert undue pressure on the cerebral neurine. Resting chiefly on the recorded results of certain experiments by Dr. Kellie, of Leith, many modern physiologists and therapeutists have maintained, that the quantity of blood in the cranium never varies; and that the brain is incompressible. Under this notion, Dr. Clutterbuck' affirmed, that no additional quantity of blood can be admitted into the vessels of the brain, the cavity of the skull being already filled by its contents. "A plethoric state or overfulness of the cerebral vessels altogether, though often talked of, can have no real existence; nor on the other hand can the quantity of blood within the vessels of the brain be diminished; no abstraction of blood, therefore, whether it be from the arm, or other part of the general system, or from the jugular veins (and still less from the temporal arteries), can have any effect on the blood vessels of the brain, so as to lessen the absolute quantity of blood contained in them." Similar views were maintained by Monro Secundus, Dr. Abercrombie,-and it is affirmed by Dr. J. Hughes Bennett to be still the doctrine of "the Edinburgh school," and they seemed to be supported by the experiments of Dr. Kellie, who inferred that, "in animals bled to death, whilst all the other organs of the body are nearly emptied of blood, the vessels of the brain contain the usual quantity; but that if, previous to bleeding an animal, a hole be made in its cranium, and the brain be thus exposed, equally with other organs, to atmospheric pressure, its vessels, like those of other parts of the body, will be emptied as the animal bleeds to death." It was important to establish the truth or inaccuracy of these views-influencing, as they were calculated to do, and have done, in so essential a manner, the therapeutics of encephalic affections; and this has been conclusively accomplished by Dr. Burrows. The experiments of Dr. Kellie were repeated by him, but with opposite results; and he concludes, that it is not a fallacy, as some suppose, that bleeding diminishes the actual quantity of blood in the cerebral vessels;-that by it we not only diminish the momentum of the blood in the cerebral arteries and the quantity supplied to the brain in a given time, but actually diminish the amount of blood in these vessels. "Whether," he remarks-"the vacated place is replaced by serum or resiliency of the cerebral substance under diminished pressure, is a question into which I will not enter."

Dr. Burrows farther investigated, whether position can affect the quantity of blood in the vessels of the encephalon,-the opinion of Dr. Kellie from the results of his experiments having been in the negative. Two full grown rabbits were killed by hydrocyanic acid, and whilst their hearts still pulsated, one was suspended by the ears; the other by the hind legs. In this manner, they were left for twenty-four hours; and before they were taken down for examination, a tight ligature was placed around the throat of each, to prevent, as effectually as possible,

Medico-Chirurgical Transactions of Edinburgh, i. 2.

Art. Apoplexy, Cyclopædia of Practical Medicine, American edit., by the author, Philad., 1844.

3 Observations on the Structure and Functions of the Nervous System, Edinb., 1783. Pathological and Practical Researches on Diseases of the Brain and the Spinal Cord, Edinb., 1836, or Amer. edit., Philad.

Lectures on Clinical Medicine, p. 143.

On Disorders of the Cerebral Circulation, Amer. edit., Philad., 1848.

any farther flow of blood to or from the head, after they were removed from their respective positions. The contrast in the appearance of the two animals was striking. The one presented a most complete state of anæmia of the internal as well as the external parts of the cranium; the other a most intense hyperemia or congestion of the same parts; and these opposite conditions induced solely by posture, and the gravitation of the blood. Like results were obtained experimentally under the direction of Professor Donders. A portion of the skull of a rabbit was removed, the corresponding piece of the dura mater cut out, an accurately fitting portion of a watch-glass let into the opening, and the junction made air tight with gum. When by compressing the nose and mouth respiration was interrupted, within ten seconds the increased redness of the pia mater could be seen with the naked eye. This condition was made still more evident by the microscope; and some minutes always elapsed before the hyperemia again diminished. A dependent position of the head also increased the hyperæmia; whilst rapid abstraction of blood very distinctly diminished the diameter of the vessels.'

The erectile tissues offer a variety in the circulation, which requires some comment. Examples of these occur in the corpora cavernosa of the penis and clitoris; and in the nipple. They appear, according to Gerber, to consist of a plexus or rete of varicose veins enclosed in a fibrous envelope, with relatively minute interspaces, which are occupied and traversed in all directions by arteries, nerves, contractile fibres, and by elastic, fibrous and areolar tissue. The fibrous envelope, and trabeculae, according to Kölliker,3 contain a considerable amount of unstriped muscular fibre.

Of the particular arrangement of vessels in the corpora cavernosa of the generative organs mention will be made hereafter: the mode of termination of the arteries in the erectile tissues has not been sufficiently studied, nor are views uniform in regard to their mode of action; some being of opinion, that they afford examples of vital expansibility; but as before remarked (page 420), excitation is first induced in the nerves of the part-generally through the influence of the brain-and the turgescence of vessels is a consequence. Kölliker maintains, that the office of the muscular fibres, which pass in every direction amongst the dilated veins is to keep them compressed in the intervals of erection; and that the excitant influence to erection, which is exerted on the nervous system, either directly or through the influence of the brain, instead of causing contraction produces relaxation of the fibres, so as to admit of free distension of the cavernous vessels. It is not easy to see, however, how the nerve power sent to a muscle can cause it to become relaxed.

The arrangement of the portal system of the liver is also peculiar, and has been given already (p. 354).

1 Cited in Brit. and For. Med.-Chir. Rev., April, 1855, p. 352.

2 Elements of General Anatomy, by Gulliver, p. 298, Lond., 1842.

3 Mikroskopische Anatomie, 2ter Bd. S. 414, Leipz., 1854; or Sydenham Society's edition of his Manual of Human Histology, or Amer. edit. of the same by Dr. Da Costa, p. 637, Philad., 1854.

g. The Pulse.

We have had occasion, more than once, to refer to the subject of the pulse, or to the beat felt by the finger when applied over any of the larger arteries. Opinions have varied essentially regarding its cause. Whilst most physiologists have believed it to be owing to distension of the arteries, caused by each contraction of the left ventricle; some have admitted a systole and diastole of the vessel itself; others, as Bichat and Weitbrecht,' have thought that it is owing to the locomotion of the artery; others, that the impulse of the heart's contraction is transmitted through the fluid blood, as through a solid body; and others, as Dr. Young' and Dr. Parry,3 that it is owing to the sudden rush forward of the blood in the artery without distension.

Bichat was one of the first, who was disposed to doubt, whether the dilatation of the artery, which was almost universally admitted, really existed; or if it did, whether it was sufficient to explain the phenomenon; and, since his time, numerous experiments have been made by Dr. Parry, the result of which satisfied him, that not the smallest dilatation can be detected in the larger arteries, when they are laid bare during life; nor does he believe, that there is such a degree of locomotion of the vessel as can account for the effect produced upon the finger. He ascribes the pulse to "impulse of distension from the systole of the left ventricle, given by the blood, as it passes through any part of an artery contracted within its natural diameter." Dr. Bostock appears to coincide with Dr. Parry, if we understand him rightly, or at all. "According to this doctrine," he remarks, "we must regard the artery as an elastic and distensible tube, which is at all times filled, although with the contained fluid not in an equally condensed state, and that the effect produced upon the finger depends upon the amount of this condensation, or upon the pressure which it exercises upon the vessel, as determined by the degree in which it is capable of being compressed. Where there is no resistance to the flow of the blood along the arteries, there is no variation, it is conceived, in their diameter, and it is only the pressure of the finger or some other substance against the side of an artery that produces its pulse."

Most of the theories of the pulse take the contractility of the artery too little into account. In pathology, where we have an opportunity for observing the pulse in various phases, we meet with sensations, communicated to the finger, which it is difficult to explain upon any theory, except that of the compound action of the heart and arteries. The impulse is obviously that of the heart, and although the fact of distension escaped the observation of Bichat, Parry, Weitbrecht, Lamure, Döllinger, Rudolphi, Jäger, and others, we ought not to con

6

Comment. Acad. Imper. Scient. Petropol. ad An. 1734 and 1735, Petrop., 1740. 2 Croonian Lectures, in Philos. Transact. for 1809, part i.

3 An Experimental Inquiry into the Nature, Causes, and Varieties of the Arterial Pulse, by Caleb Hillier Parry, London, 1816; also, Additional Experiments on the Arteries of Warm-blooded Animals, &c., by Charles Henry Parry, M. D., &c., London, 1819.

Physiology, 3d edit., p. 246, Lond., 1836.

5 Grundriss der Physiologie, 2ter Band. 2te Abtheil., s. 301, Berlin, 1828. Tractatus Anatomico-physiologicus de Arteriarum Pulsu., Virceb., 1830.

clude, that it does not occur. It is, indeed, difficult for us to believe, that such an impulse can be communicated to a fluid filling an elastic vessel without pulsatory distension supervening. In opposition, too, to the negative observations of Bichat and Parry, we have the positive averment of Dr. Hastings, and of Poiseuille, Oesterreicher, Ségalas, and Wedemeyer, that the alternate contraction and dilatation of the larger arteries were clearly seen.2 M. Flourens encircled a large artery with a thin elastic metallic ring cleft at one point. At the moment of pulsation the cleft part became perceptibly widened.3

The pulsations of the different arteries are pretty nearly synchronous with that of the left ventricle. Those of the vessels near the heart may be regarded as almost wholly so; but an appreciable interval exists in the pulsations of the more remote.

We have remarked, that the arterial system is manifestly more or less affected by the nerves distributed to it; that it may be stimulated by irritants, applied to the great nervous centres, or to the nerves passing to it; and this is, doubtless, the cause of many of the modifications of arterial tension, noticed in disease. Inflammation cannot affect a part of the system, for any length of time, without both heart and arteries participating, and affording unequivocal evidence of it. This, however, is a subject that belongs more especially to pathology.

The ordinary number of pulsations, per minute, in the healthy adult male, is from seventy to seventy-five; but this varies greatly according to temperament, habit of life, position, whether lying, sitting, or standing, &c. Dr. Guy, from numerous observations, found the pulse, in healthy males, of the mean age of 27 years, in a state of rest, 79 when standing; 70, sitting, and 67, lying; the difference between standing and sitting being 9 beats; between sitting and lying, 3 beats; and between standing and lying, 12 beats. When all exceptions to the general rule were excluded, the numbers were;-standing, 81; sitting, 71; lying, 66;-the difference between standing and sitting being 10 beats; between sitting and lying, 5 beats; and between standing and lying, 15 beats. The effect, produced upon the pulse by change of posture, Dr. Guy ascribes to muscular contraction, whether employed to change the position of the body, or to maintain it in the same position. In children, the difference between the pulse in the sitting and lying posture is often very marked. In a boy, six years of age, observed by the author, it amounted to fifteen beats; and Dr. Evanson' states, that he has often found the pulse-which at night (during sleep) was 80, full and steady-up to 100 or even 120 during the day, small and hurried, and this in children six or seven years of age, and in perfect bealth.

In some individuals in health, the number of beats is singularly few.

1 Répertoire générale d'Anatomie, &c., par Breschet, 1829, tom. vi. and vii., Magendie's Journal de Physiol., viii. and ix.

and

2 For a mode of estimating the arterial distension, see Poiseuille, in Magendie's Journal de Physiologie, ix. 44, and Jules Herison's description of an instrumentSphygmometer-which makes the action of the arteries apparent to the eye.

3 Kirkes and Paget, Manual of Physiology, 2d Amer. edit., p. 98, Philad., 1853.

4 Guy's Hospital Reports, No. vi., April, 1838, p. 92.

5 Practical Treatise on the Management and Diseases of Children, by Messrs. Evanson and Maunsell: Amer. edit., by Dr. Condie, p. 19, Philad., 1843.

The pulse of a person known to the author was on the average thirtysix per minute; and Lizzari' affirms, that he knew a person in whom it was not more than ten. It is not improbable, however, that in these cases, obscure beats may have taken place intermediately, and yet not have been detected. In a case of pericarditis, in which the author felt great interest, the pulse exhibited a decided intermission every few beats, yet the heart beat its due number of times; the intermission of the pulse at the wrist consisting in the loss of one of the beats of the heart. It was not improbable but that in this case the contractility of the aorta was unusually developed by the inflammatory condition of the heart; and that the flow of blood from the ventricle was thus occasionally spasmodically diminished or entirely impeded. On the other hand, the natural pulse is, at times, far above the average,-100 and upwards in the minute. It is affirmed that the pulse of Sir William Congreve2— the inventor of the well-known Congreve rockets-when he was in apparently good health never fell below one hundred and twentyeight beats per minute. The quickest pulse, which Dr. Elliotson3 ever felt, was 208, counted easily, he says, at the heart; though not at the wrist.

The pulse of the adult female is usually from ten to fourteen beats in a minute quicker than that of the male. In infancy, it is generally irregular, intermitting, and always rapid, and it gradually becomes slower in the progress of age. It is, of course, impossible to arrive at any accurate estimate of its comparative frequency at different periods of life, but the following average by Heberden, Sömmering, and Müller, have generally been received. They are inaccurate, however, in regard to old age, more especially.

A nearer approximation is given by Dr. Guy in the following table:

Raccolta D'Opusculi Scientific., p. 265; and Good's Study of Medicine, Physiolo gical Proem to class iii. Hæmatica. See Cases of Slowness of Pulse, by Mr. Mayo, Lond. Med. Gaz., May 5, 1838, p. 232.

2 Adventures and Recollections of Colonel Landmann, late of the Corps of Royal Engineers, i. 12, London, 1852.

3 Human Physiology, p. 215, London, 1840.

Med. Transact., ii. 21.

Handbuch der Physiologie, Baly's translation, p. 171, London, 1838.