accurate knowledge of the nature of an impression, by having it made on different parts of the skin in succession. By a peculiar internal feeling, called the muscular sensation, informing us of the extent of muscular contraction, we come to know the direction and space in which our limbs are moved; and every one knows that this feeling is of very considerable importance in aiding the sense of touch, and in improving that kind of touch frequently distinguished in this country by the term Tact. It has already been remarked, that it is not unfrequently difficult to discriminate whether we judge of the qualities of a surface by the sensibility of the skin, or by the muscular sensation. We can in general tell immediately the direction in which any one pulls the hair of our head; but the knowledge of this direction is not derived, as might be supposed, from the sense of touch, but depends on an exertion of the muscles of the head, which is immediately and insensibly made with the view of resisting the motion of the head, which without it would occur. On fixing the whole head, it will be found that the power of distinguishing the direction still remains, though in a less degree. This seems to depend on the position of the skin in the neighbourhood being altered by traction, for when we fix the skin the power of distinguishing the direction in which the hair is pulled entirely disappears.

Another illustration of this is obtained from the following experiment. Shut the eyes, hold the hand steady, and let some one touch your fingers with, and carry along their points various substances, as paper, glass, metal, wood, quill, leather, linen, silk, or velvet; you will be surprised how often you mistake the one for the other, according as they are more or less lightly pressed against the fingers. Metals when of the same temperature as the hand can scarcely be distinguished from glass and other substances with a smooth surface. When the finger of one person is conducted by another into a fluid, the slight pressure over a considerable surface informs him of its presence. If a person draws a plane surface along the finger of another, pressing at first gently, then gradually more strongly, and again gently, the feeling of a convex surface will be communicated to the finger, and that of a concave surface may be given by the greatest pressure being made at each end.

Professor Weber next relates some experiments which he performed with the view of ascertaining how far we are capable of judging of the Weight of bodies by the sense of touch in the skin, and how far it is necessary that we should be assisted also by the muscular sensation; for it is obvious that in general we make use of both these means to obtain a correct estimate of weight.

He found that when two equal weights are placed on corresponding parts of the skin, he might add to or subtract from one of them a certain quantity without the person on whose skin they were laid being sensible of any change or inequality in them. He ascertained that when the hand or any other moveable part of the body is laid quite inactive on a table, a much greater change can be made in the relative weight of the two bodies, without its being perceived, than when the limbs are free and capable of muscular exertion: that thirty-two ounces or drachms, for example, may be altered by from eight to twelve, when the hand is motionless and supported, but only by from one and a half to four, when the muscles are in action; and hence Professor Weber infers, that the measure of weight by the touch of the skin alone is more than doubled by the assistance of the muscular sensation.

By these experiments it was found that the lips estimate weight more correctly than any other part of the body: the fingers and toes may be reckoned next, the second phalanx being inferior to the third, and the first to the second: the palm of the hand and sole of the foot, especially the parts covering the ends of the metacarpal and metatarsal bones, possess also a considerable power, while the back, thorax, abdomen, scapulæ, arms, legs and occiput have very little power of estimating weight; which observations obviously show a considerable correspondence between those parts of the skin possessing the most acute sense of touch, and those estimating weights most correctly.

Professor Weber attributes to a more acute sense of touch in the left arm, the circumstance, that to most persons weights appear heavier to the left than to the right arm. This is no doubt to a certain extent caused by the common preponderance of the muscles of the right arm over those of the left; but Professor Weber states that he has also proved that in a large proportion of the individuals on whom he has experimented, the sensibility of the skin on the left arm is greater than that on the right, and he has found, that though the hand is not assisted in any degree by the muscular action or sensation, as when it is steadily supported, weights still appear heavier to the left than to the right Of fourteen individuals of different classes of society, eleven found the weights heaviest in the left hand, two heaviest in the right, and in one there was no difference between the right and left. He also ascertained that this acuteness of touch in recognizing weight, resides not only in the left hand but also in the left foot and scapula.

arm.

The weights employed ought to be made of the same material, and must present the same size and form of surface to the skin. In order to insure this, and to correct the difference of temperature, it is well to interpose similarly shaped pieces of pasteboard between the weights and the skin.

In concluding this account of Professor Weber's researches, which I regret I have been obliged to shorten too much, I may state that I have repeated a considerable number of the experiments on the comparative sensibility of different parts of the skin on my own person, as well as on other individuals, and have obtained very nearly the same results. The acuteness of the sense of touch over the whole skin seems to me to vary more or less in different individuals; but I have not observed any striking deviations from the results recorded in Professor Weber's papers, in respect to the relative acuteness of this sense in the different regions of the body.

ART. XI.-Note on the Modes in which Death takes place in Cholera. By SAMUEL GASKELL, Esq. Stockport Infirmary, being Appendix to the paper No. vi. p. 52.

IN

N the cases referable to the first form of the disease, the fatal termination is gradual and almost imperceptible; the patient remains in a pulseless state for a longer or shorter period, according to the intensity of the attack; the respiration becomes quick and short, but easy and regular; at length the impulse of the heart is no longer perceptible, and the respiratory action gradually ceases; a few respirations are always observed after the cessation of the heart's action. During the progress of these changes the body is motionless, and it is difficult to determine at what precise period the vital actions have ceased.

In the cases referable to the second form, the respirations are heaving and laborious, the action of the heart tumultuous, the pulse oppressed, but rarely imperceptible. The respirations become more laborious and heaving, and the interval between each inspiration is gradually prolonged, until the action ceases altogether. Shortly after the last expiration, a violent throbbing is observed in the præcordial region, accompanied with a fluttering in the course of the carotid and subclavian arteries. The patient, up to the time of death, is restless, and appears much distressed by a sense of oppression. The body after death is much darker, but less shrunk in this than the other class of cases.

The most superficial observer at once detects a striking distinction between these two modes of fatal termination. It is almost needless to add, that in the first class of cases death occurs by failure of the heart's action, in the second, by obstruction to the respiratory functions. We thus perceive, that from the first symptom to the termination in death or recovery, a division of cholera into two classes is strikingly indicated; but a stronger reason for such a classification may be urged, if we take into account the very opposite kind of treatment required in these two states of the system.*

For Mr Gaskell's remarks on the treatment, see "Observations on the Cholera of Manchester by Dr Gaulter."

[95]

PART II.

CRITICAL ANALYSIS.

ART. I.-The Cyclopædia of Practical Medicine. Edited by JOHN FORBES, M. D. ALEXANDER TWEEDIE, M. D. and JOHN CONOLLY, M. D., &c. Vol. II.

IN resuming our account of the contents of this work, we

begin by laying down the general principle formerly announced, that it is quite superfluous to advert to every article; and we shall merely direct the attention of our readers to those which appear either, in regard to the subjects of which they treat, or the manner in which they are treated, to merit most attention.

We shall also in this account adhere to the arrangement formerly observed, that, namely, of identity of authors, and similarity or affinity of subjects.

In Materia Medica we find two instructive articles on Emetics and Expectorants, by Dr A. T. Thomson.

In the former article the author, after a view of the different theories which have been maintained on the mechanism of vomiting, by Chirac, Litre, Lieutaud, Magendie, Sir Charles Bell, and Dr Marshall Hall, gives one of his own, in which, modifying the sentiments of the latter author, he infers, that the act of vomiting is the result of the simultaneous action of all the muscles of respiration, at a moment when the glottis is shut, and offers resistance to the ascent of the diaphragm,-as, in short, an expiratory effort, but which is abortive by reason of the glottis being closed.

In the article on Expectorants the author divides that class of medicines into two orders, topical and general expectorants. To the former he refers all those agents which are applied to the surface of the bronchial membrane in the form of vapour, as benzoin, acetic acid, chlorine, the fumes of tar and undressed wool, and the fumes of tobacco and stramonium,-and emetics which operate, he conceives, by mechanical compression; and under the latter head he arranges all those substances which, being received into the circulation, act thereby on the bronchial membrane, or act on that membrane by previous influence on the gastric. This order contains, 1st, all the emetic expectorants, as ipecacuan and

squill, the stimulating gums, as myrrh, ammoniac, assafoetida, styrax, benzoin, balsam of Tolu and Peru, and Copaiba, and such substances, as horehound, colt'sfoot, and Iceland moss; and 2d, the nauseating expectorants, as the antimonials. The latter, we conceive, might have been advantageously arranged with the emetic expectorants, ipecacuan and squill, since both seem to operate in the same manner, by modifying the circulation of the gastric mucous membrane, and thereby that of the bronchial mucous membrane.

The article is one of much interest; and the concluding observations on the circumstances regulating the selection of emetics deserve the particular attention of the practitioner.

The articles Emphysema, Emphysema of the Lungs, Empyema, Displacement of the Heart, and Hypertrophy, are very ably treated by Dr Townsend.

In the first article the observations on spontaneous Emphysema are extremely valuable, in so far as they present a short general view of the scattered facts recorded on the nature and causes of that process in the living body. This depends either on decomposition of the fluids, when it cannot take place in the living body without the occurrence of gangrene, general or local, or at least decomposition of the contents of the cavities, as the stomach and intestines, or on the secretion of air from some of the membranous tissues, as in the case of the cellular membrane.

In that on Emphysema of the Lungs, the author gives an account of the causes and nature of that affection much after the manner of Laennec.

In the article on Empyema, or effusion of fluid, purulent, sero-purulent, or bloody, into the cavity of the pleura, Dr Townsend gives a very excellent account of the causes, various forms, effects, and characteristic symptoms of that affection. From the results of ten cases of empyema, in which the operation of paracentesis of the chest was performed in London, chiefly under the direction of Dr Thomas Davies of the London Hospital, and in which eight recovered, Dr Townsend properly infers, that the operation should always be performed when the disease can be positively recognized, and when the symptoms are urgent. In cases of pneumathorax, in which the pleuritic inflammation is too often the effect of the progressive destruction, occasioned by tubercular softening, it appears to be less eligible. In nine cases in which the operation was performed in London, all died; and in all the pneumathorax was complicated with, or, in other words, had arisen from tubercular disease of the lungs. In three cases of hydrothorax in which it was performed, the symptoms underwent temporary