to the same amount would require three times as much blood to be taken by small bleedings for its production: giving rise to a greater loss of red globules, a slower reparation, and a more tedious convalescence. The smaller bleedings allow of an imperfect reparation in the intervals, but the greater tolerance thus induced is a deceptive phenomenon when full bleeding is indicated, although, under other circumstances, it may be made usefully available.

"Free abstraction is indicated when we have to do with a commencing inflammation of a severe character in a robust individual; while the smaller loss is indicated in feeble subjects, liable to disturbances of the circulation, or endowed with great nervous susceptibility. In case of collections of corrupt matters (as abscess, open cancer, gangrenous foci, &c.), a large abstraction is never advisable; while in marked plethora (dense blood too rich in globules) it is indicated. Free abstraction, developing in great part also a mechanical effect, is required in those hydraulic derangements of the circulation arising from remora, or partial fulness of vessels; and in cases in which it is important to excite, at whatever cost, a rapid absorption of effused fluids. Small, interrupted, emissions, will, on the other hand, be always preferable, when, in a diseased state of the circulatory organs, rapid changes of the fluid in them, or a difficult assimilation of fluids absorbed without much election, is to be feared."-Vol. 121, p. 281.

(4). The phenomena observed in the excessive loss of blood in hæmorrhages teaches us two things. First. That a profuse loss of blood is best borne when taken so as to imitate in some degree the stillicido of hæmorrhage than if abstracted rapidly by a free bleeding. Quesnay showed that, if a large opening be made in a vein, we can regulate the flow by means of a bandage just as we please; and, if it be so managed that about six ounces only are lost in the hour, the patient will be found able to tolerate such an evacuation for a very long period; so that at the end of the 24 hours, perhaps, 12lbs. (of 12 ozs.) may have been taken.

"In suffocative angina, in grave pulmonary congestions threatening asphyxia, in certain very rapid cerebral phlegmasiæ, and, above all, in cases in which energetic and prompt treatment is demanded, while the tendency of the patient to syncope impedes its adoption, or gives rise to functional disturbances it is desired to avoid, this means of bloodletting becomes of great use."

Secondly. When we are desirous of arresting a hemorrhage, we may often accomplish this by drawing a small quantity of blood in a large stream; so that, with no great loss and endured for a very short period, coagulation at the mouths of the affected vessels may be promoted. This prevents that despoiling of the blood and exhaustion of the strength which supervene on a constant drain of blood, surprisingly as the system may seem to tolerate this.

"And it is not unreasonable to suppose that many cases of metrorrhagia, hæmoptysis, epistaxis, and even hæmorrhage from mechanical lesions of internal vessels, to combat which a number of interrupted bleedings have been in vain employed, besides a variety of cold and hæmostatic applications, would have been easily checked, had the patient been boldly bled, ad deliquium, at the commencement."

(5). It is a well-established fact, that excessive bloodletting, and even moderate in subjects having diseased circulating organs, give rise to dropsical effusions. This does not seem to be dependent upon a disturbed state of the circulation, or on any venous stasis, but may be, in our author's

1847]

Practical Applications.

325

view, referred to three causes. (a). In such persons there is induced in the remaining mass of the blood the same serious modifications observable in Bright's disease-watery dilution, diminution of globules, and great impoverishment of albumen. (b). After repeated bleeding, the secretory organs become inert and indolent. (c). The last cause, probably the foundation of the other two, is found in the diminished density of the blood, allowing it to yield more readily to the capillary attraction of the membranes, and thus give rise to an exosmosis or hydropic effusion which would not occur in denser blood.

This leads us to an appreciation of the advantageous employment of blisters for the cure of dropsies dependent upon a modification of the crasis of the blood. By free vesication we may take from a patient from 8 to 16 ozs. of a fluid which is a species of diluted blood-"thus evacuating all the materials of the blood except the red globules, practising, in fact, a white bloodletting, acting upon the remaining mass in a completely opposite manner to its spoliation by bleeding. This is probably the chief reason for the great assistance all practitioners have derived from the use of blisters at the close of the treatment of inflammation, when much blood has been abstracted, and the removal of a commencing effusion is desired. How can we in such cases better remedy both the effects of the disease and the treatment than by the use of blisters ?" Large, flying blisters are best adapted to this end.

(6). The attenuation of the blood by repeated bleeding, its deprivation of red particles, and the excess of fibrine, induce an amount of crust or buffiness which would not result from the mere slow coagulation of phlogosis. A false buff, or a buffiness from bleeding, may thus become very marked, and a practitioner ignorant of its mode of generation may draw very unsafe indications from its inspection.

(7). The question whether bleeding, used immoderately, or in cases in which it is not strictly necessary, may not give rise to a necessity for ils more frequent repetition, a habit, is answered affirmatively for the following

reasons.

-* (a). That it accustoms the organism to tolerate a change in the composition of the mass of the blood which renders the effects of subsequent abstractions less sensible. (b). It habituates it to the renunciation of natural modes of restoration, or such as, by means of a little expectation, might easily be made to appear: so that after one, two, or three morbid emergencies, cured in this oblique manner, on a fourth occurring, bleeding becomes inevitable. (c.) A reparation of blood greater than the loss is sometimes provoked, giving rise to a species of false plethora."

(8). Not only may excessive bleeding render convalescence tedious, and give rise to cachexia and vices of innervation difficult of removal, but it may lead to a fatal termination of the malady, which would not otherwise have taken place. The effects of repeated bleeding are accumulative; and the apparent toleration exhibited by the individual in so few signs being offered of disturbed functions is a far less faithful guide than is the examination of the changes operated in the blood. These are progressive, as the fluid cannot be re-constituted when the abstractions succeed each other at short intervals. The effect does not terminate with the bleeding; for the absorption of new materials, and the influence of these upon the blood, continue long after.

To the remaining section on the "Effects of Bloodletting upon the Motion of the Blood," we have space only to allude. The experiments of De Heide, Haller, and Spallanzani upon cold-blooded animals, together with his own on horses, and his observation of man suffering under disease, lead the author to the general conclusions that the immediate effect of bloodletting both on man and animals is the production of a greater quickness of the pulse: but, in both, when carried to syncopy, it diminishes the number of beats. Repeated abstraction not only tends to accelerate the circulation, but also, in a still greater degree, the respiration; and this increased frequency of pulse and respiration are among the effects of bloodletting latest in disappearing.

This brings Dr. Polli's valuable labours to a conclusion, as terminating the investigation of the immediate modifications which the blood undergoes. To complete the subject, the effects which the fluid so modified produces on the various organs has yet to be examined; and we hope this able enquirer will not recoil before a task he declares too difficult and laborious for him to encounter. Certain are we that a more careful and talented investigator will not be found; and in no country is such an enquiry more urgently called for than in Italy, where it seems to us that this therapeutical agent is employed with a most unjustifiable freedom and rashness.

THE PHYSIOLOGICAL ANATOMY AND PHYSIOLOGY OF MAN. Part the Third. By Robert Bentley Todd, M.D., F.R.S., Professor of Physiology, and William Bowman, F.R.S., Demonstrator of Anatomy in King's College, London. John W. Parker, 1847.

We are happy to announce the appearance of the first portion of the second and concluding volume of this important work; and trust that the remaining part will, as the advertisement states, be speedily published. The part before us contains a very interesting account of the organs of smell, vision and hearing, including their structural anatomy and physi ology; the anatomy and functions of the several encephalic nerves of the great sympathetic, are next given; and, lastly, the ogans of digestion are partly investigated. We propose to lay before our readers a concise account of the many new facts connected with the Organs of Sense, with which the authors have enriched their pages; but to accomplish this object, it will be necessary to refer to the latter part of the first volume, containing the Organs of Touch and Taste, published about two years since, and which we have not hitherto had an opportunity of noticing. We must, however, in the first place congratulate Dr. Todd and Mr. Bowman, and especially the latter gentleman, that they have been able, by their admirable and skilful observations, to throw so much new light on the delicate organization of many important parts; a merit this of no ordinary kind, when it is recollected that the intimate texture of the organs to which we refer, has been made the subject of laborious and repeated investigation by several of the most distinguished microscopists of Europe.

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On Sensation and Perception.

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Without entering into any metaphysical speculations, we may briefly consider, as constituting the most fitting introduction to the subject matter of the work before us, the nature of sensation in general, and especially the relations existing between the mind and the external objects of sense; and we are the more strongly prompted to this, by the consideration that some of the errors of former times still linger among us; and especially because, although the mechanism of perception, as we may for the moment be permitted to term it, is tolerably well understood by physiologists, it is but very imperfectly apprehended by persons in general, even in many instances by those who have paid some attention to the subject. The authors preface their account of the special senses by the following definition :

"Sensation is an affection of the mind occasioned by an impression made on certain parts of the nervous system, hence called sensitive. A state of the sensitive organs, and a corresponding perception by the mind, must concur to produce sensation: either condition may exist alone, but then the phenomenon is not a true sensation, in the acceptation here given to the word. Thus, light falling on the eye in sleep excites the whole visual sensitive apparatus, while the organ of perception is inactive: on the other hand, in dreams, vivid pictures of objects float before the mind, and are referred by it to the external organ, which may be all the while entirely quiescent." Vol. Í, p. 402.

Sensation is thus properly regarded as a phenomenon of consciousness, an acceptation of the term which definitively excludes what has been called, after Bichat, organic sensibility. But, although the authors are correct as far as they have gone, they have not explained what it is which, in the act of perception, is presented to the mind; an explanation which is the more demanded, since, in a passage immediately following, it is noticed as a remarkable circumstance that "the organ of the mind itself does not appear capable of undergoing sensory excitement;" or, in other words, of receiving directly impressions from the external objects of sense. The fact is that, in every kind and form of sensation, the mind does not take cognizance of the properties of external objects, but of the altered state of the nerve of sense induced by the impression made upon it, as by light, sound, &c. This truth, which is essential to a just appreciation of the whole matter, is thus clearly stated by Professor Müller in his Physiology: "sensation consists in the sensorium receiving, through the medium of the nerves and as the result of the action of an external cause, a knowledge of certain qualities or conditions, not of external bodies, but of the nerves of sense themselves." In order then to excite the act of perception, the impression must in every instance be made on a nerve of sense; and this being so, the wonder ceases as to the cerebral hemispheres, the seat of all perception, being themselves incapable of perceiving impressions made directly upon them by external bodies. But we learn, moreover, from this that, although many persons conceive that what are called "subjective" and "objective" sensations are essentially distinct modes of sensation, in one case the mind taking cognizance of a condition of the nerve, and in the other of the quality of the external object, they in reality only differ from each other as to the manner in which the nerve is excited; in subjective sensation, a stimulus of an unusual kind is applied, as when the retina is pressed upon by the finger applied to the globe of the eye, or when the auditory nerve is excited by some deranged state of the circula

tion inducing tinnitus aurium; whereas, in objective sensation, what is considered the natural stimulus is applied.

In describing the organ of taste, the authors have given a most interesting account of the various forms of papillæ placed on the tongue. The most remarkable fact is, that the conical or filiform papillæ, distinguished on the dorsum by their whitish colour, are not only provided with an abundant epithelium frequently composing two thirds of their length, but actually present, at least a few of them, minute hairs, the largest of which are of an inch long, and from too of an inch thick. There can be little doubt that these papillæ are subservient rather to touch than to taste; and they may, by their structure and partial mobility, fulfil the office assigned to them by the authors, that, namely, of directing the muscular actions of the tongue during mastication, and thus promoting the almost manual dexterity of the organ in dealing with minute particles of food.

The chapter treating on the Minute Anatomy of the Eye, contains several new facts, which must prove most interesting as regards both the functions and diseases of the various component parts of this must complex organ. In the first place, as respects the cornea, it may not be superfluous to state, although the greater part of this has been for some time known, that it is composed of five coats or layers, clearly distinguishable from each other; these are the conjunctival layer of epithelium, the anterior elastic lamina, the cornea proper, the posterior elastic lamina, and the epithelium of the aqueous humour, or posterior epithelium. The conjunctival epithelium may always be obtained from a fresh eye by gently scraping the surface of the cornea; it consists of three or four layers of superposed particles, inclining to the columnar form where they rest on the anterior elastic lamina. "It is in this epithelium that particles driven with force against the eye generally lodge, and it is easily detached by the instrument used to extract them. Vessels shooting into the cornea in disease* lie under it, and small ulcers are formed by its destruction."—Vol. II., p. 20.

The cornea proper, or lamellated cornea, consists of a peculiar modification of the white fibrous tissue, which is continuous with that of the sclerotic. The lamellæ, sixty and upwards in number, formed of these fibres, are intimately united to one another by processes of a similar texture, which produce, however, a very delicate, tubular structure, now for the first time thus described.

"The resulting areolæ, which in the sclerotic are irregular, and on all sides open, are converted in the cornea into tubular spaces, which have a very singular arrangement, hitherto undescribed. They lie in superposed planes, the contiguous ones of the same plane being for the most part parallel, but crossing those of the neighbouring planes at an angle, and seldom communicating with them. The arrangement and size of these tubes can be shown by driving mercury, or coloured size, or air, into a small puncture made in the cornea. They may also be shown under a high power by moistening a thin section of a dried cornea, and opening it out by needles. The tissue forming the parietes of these tubes is membranous rather than fibrous, though with the best glasses a fibrous striation may be frequently seen, both in the laminæ separating the different series of tubes, and in that dividing those of the same layer from each other. By acetic

* In health it is now known that the cornea contains no blood-vessels.