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in its alphabetical place or places. It should surprise no one that the student of Newton and Laplace may be even obliged to make an addition to his studies, the benefit from which he shares in common with those of lower intellectual pursuits. We have seen that Newton himself judged such an accompaniment desirable ; and it has been conceded by many admirers of the Cambridge system, that analysis was too exclusively pursued, to the neglect of independent means of illustration and evidence. We can only hope the present example will be imitated; and that every branch of physical science will be examined for the purpose of finding out to what extent a course similar to that struck out by Professor Airy is possible.

To those organs of public opinion which have sneered at cheap works, because they are cheap, the present treatise will be a useful lesson; and as a predecessor of Professor Airy remarked, in another case, they may read it, not unprofitably, since, if it does not prove the cure of prejudice, it will be at least the punishment.' But there may be another and a higher class, better worth the bringing to a proper view of what they can do, and ought to do, for the promotion of habits of sound reasoning among their fellow-countrymen : and surely the example of Professor Airy and Sir John Herschel in England, with that of M. Arago in France, ought to induce those who are able to teach, to look upon such sneers with indifference equal to the scorn with which they are regarded by those who are willing to learn. Let them leave such little prejudices to the little world they were made for : and comparing the state of instruction now existing, with that of a preceding age, let them not presume to say how far knowledge may or ought to be extended, but furnish all the means in their power, and settle that point, as they determine an unknown fact in astronomy, by observation.

THE PRINCIPLES OF PHYSIOLOGY. The Principles of Physiology applied to the Preservation of

Health, and to the Improvement of Physical and Mental Education. By Andrew Combe, M.D. Edinburgh, Black.

London, Longman and Co. 1834. Men generally read scientific books either with a desire to ascertain the progress of knowledge, or with the view of determining how far new discoveries, or the new application of principles long established, may assist them in the pursuit in which they are engaged. The work which we are about to describe is addressed to neither of these classes; and, althoug

it may be read with profit by both, the aim of the author has been to speak to the whole community, and especially to those who, whether called the educated or uneducated, are destitute of all useful and practical information as to the means of preserving their health. The style is so plain, and the arguments so convincing, that no person can fail to perceive how intimately his health and happiness are connected with the truths which the author has endeavoured to enforce. Physiological science has hitherto been confined to a particular profession; and this exclusive knowledge is sometimes defended upon the absurd notion that it would be difficult or impossible, and dangerous if possible, to circulate knowledge of this kind among people generally-among those, in fact, whom it most intimately concerns.

The work of Dr. Combe is to a great extent, we think, original. The principles are those which have long received the sanction of the majority of physiologists; the facts are old, the illustrations are familiar: but the author has shown how these generally acknowledged principles can be applied by every individual to the preservation of health, the great source of all happiness. It has been known for half a century that the action of the lungs, called respiration, alters the constitution of the atmosphere, and that we walk by means of the alternate contraction and relaxation of certain fleshy parts called muscles, which act as levers upon the solid parts of the frame; but it has not been shown till now, that upon the breathing of pure air and the taking of proper exercise depend, in a great measure, not merely the preservation of the natural form of the body, the vigour of the constitution, and the duration of life, but the general capabilities for education and mental cultivation. The author has shown in this work, that he is well aware of the inefficacy of vague generalities; of the uselessness of merely stating laws or principles, and the results of a violation or disregard of these, without dwelling upon the process by which these results are brought about. He has described in succession the different organs of which the body is composed; from their anatomical structure he passes to the function which they perform, the relation which this bears to the rest of the system, the manner in which it is affected by external circumstances, the use or duty to which each is subservient; and, lastly, he contrasts the consequences which flow from an ignorance or disregard of these circumstances, with those advantages which naturally follow from that line of conduct which an acquaintance with them suggests. For instance, he treats of the muscular system as an agent, the nature of which must be explained to all men, before they çan adequately appreciate or employ to advantage the powers which it confers. He first describes an individual muscle as a bundle of fleshy fibres or threads, distinct and separated from each other by a thin membrane, but all inclosed in one common sheath, and acting in concert. These bodies are attached at two points to the bones, and their action consists in contracting, in diminishing their own length, and thereby bringing the two points nearer to each other. The chief purpose of all such contractions is to enable us to move either the whole or a part of the body in compliance with the will; but, in effecting this end, additional results are produced which appear to be almost of equal importance, and highly conducive to the healthy condition of the organs themselves. The flow of the blood is thus assisted through the remote and minute vessels by the pressure on their exterior, and the processes of digestion, respiration, and absorption are likewise materially promoted.

That muscular action may be healthy and vigorous, it is of course necessary that the fibres should be strong and duly stimulated. It has been proved, that whenever a muscle is frequently used, its fibres increase in thickness within certain limits, and become capable of acting with greater force and readiness; and that, on the other hand, when a muscle is rarely called into exercise, its volume and power decrease in a corresponding degree. Their power again is known to correspond to the quantity of blood which they receive, and this is regulated by the extent and energy of their action. When any part, accordingly, is deprived or stinted of its usual supply of blood, it very soon becomes weakened, and at last loses the power of action, although every other condition required for its performance may remain unimpaired. If these are laws established by nature, it may be expected that certain consequences, or penalties, will follow any acts or habits which tend to the infringement of the conditions which they impose. Hence all classes, and especially the youthful manufacturing population and the inmates of boarding-schools, who fail to call the muscles frequently and fully into action, suffer not merely from the weakness and imperfect development of these organs, but from the debility and disease of the general system. The movements of the muscles are, however, governed and guided by the nerves; and by introducing this new ingredient into the consideration of the subject, new conditions necessarily arise. The nerves are represented as white pulpy cords, originating in the brain or spinal marrow, and conveying sensations to, or volitions from, the mind. Whenever this connexion or communication is interrupted, two consequences ensue,-the mind no longer receives impressions from without, nor can it excite the muscles to action. Causes, then, which injure or destroy any one of the links of this chain, subvert the whole series of functions with which it is connected as effectually as if the whole had been destroyed. If the brain or spinal marrow be injured by blows, disease, ardent spirits, or any other poison, voluntary motion ceases, or is suspended ; if the nerves be divided while the brain and muscles are sound, the same result takes place; and if the muscles be emaciated, languid, and unaccustomed to exercise, the mind may determine, and the nerves may convey the determination, but it will be in vain.

To the healthy and vigorous performance of muscular action, which consists in the alternate contraction and relaxation of the fleshy fibres, it is obvious that the co-operation of the nervous and circulating, as well as the muscular, systems is essential. Exercise affects these in the same manner, giving strength to the organ, and intensity to the function; but on the muscular system the effects are more palpable. If neglected, diminished bulk and strength, languor and an incapability of sustained motion, are the inevitable results; if carried to excess, fatigue, exhaustion, general debility, and some local injury may follow; whereas, if regulated by the laws and limits so obviously laid down by nature, the whole system is invigorated and consolidated, rendered competent for that physical exertion which is required in every situation, and its sphere of enjoyments and of duties is increased. These principles, selfevident although they seem, have, however, been generally overlooked, but especially at that time and in those circumstances during education, when their application is chiefly required, and would prove most productive of benefit. This fact is illustrated in a melancholy manner by attending to the plan often pursued in female boarding-schools. The body is kept for many hours perfectly motionless, in an erect, stiff, constrained, and fatiguing attitude,-a punishment being awarded should the back bend, in other words, should a muscle seek relief in relaxation : those of the back are retained as long as possible in a state of tension, at first by the exercise of the will, and when that fails, by back-boards, straps, stays, &c. While this position is preserved, the spine is of course perpendicular, supporting by its still incompletely ossified bones the weight of the head and the upper parts of the chain of bones of which it consists. This painful exertion, imposed as if muscles were exempt from fatigue, is not limited to any particular occasions, but is required, whatever other duty or employment may be prescribed; so that whether music, drawing, or sewing occupy the mind and hands, the same rigid, immoveable carriage must be observed. Were this severe discipline frequently interrupted, were the muscles permitted to

rest and relax, while other sets were freely and fully moved by walking, dancing, romping, or any amusement requiring agility in the play-ground, the baneful effects might be obviated or mitigated ; but such is not the case, for in many institutions such natural ebullitions would be regarded as a violation of discipline, and as a breach of that dignity and decorum incumbent on the sex. ' How great the baneful effects are, to which allusion has been made, may be collected from the following quotation :-'We lately visited,' says a writer of great authority on this subject, 'a boarding-school containing forty girls; and we learnt on close and accurate inquiry, that there was not ONE of the girls who had been at the school two years (and the majority had been as long) that were not more or less crooked. And we can assert, on the same authority of personal observation, and on an extensive scale, that scarcely a single girl (more especially of the middle classes) that has been at a boarding-school for two or three years, returns home with unimpaired health.' * We have thus attempted to paraphrase a few passages in Dr. Combe's book, in order to show its general scope and tendency, the practical manner in which the subjects it embraces have been treated, and the important bearings which these have on the present condition and prospective improvement of mankind. The same attention to utility characterises every page. The description of the layers of which the skin is composed, their relation to perspiration, and the consequences of the suppression of this secretion, serve as an introduction to the consideration of this tissue as a regulator of heat, to some remarks on the mortality of infants from ignorance of this fact, and to the inculcation of the universal necessity for ventilation and ablution.

Indeed, that part of Dr. Combe's work which treats of the action of the skin seems to us one of the most important, both on account of the magnitude of the evil which results from inattention to the proper functions of this part of the body, and from the simple nature of the preventives or remedies which are at the command of every person.

• If one-tenth of the persevering attention and labour bestowed to so much purpose in rubbing down and currying the skins of horses were bestowed by the human race in keeping themselves in good condition, and a little attention were paid to diet and clothing, colds, nervous diseases, and stomach complaints would cease to form so large an item in the catalogue of human miseries. Man studies the nature of other animals, and adapts his conduct to their constitution; himself alone he continues ignorant of, and neglects. He considers himself as a being of a superior order, and not subject to

* Forbes, in Cyclopædia of Practical Medicine.'

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