terranean parts of stems which are not green are in the same condition as roots. Flowers not only part with a portion of their carbon to the oxygen of the air, but exhale a little nitrogen; the quantity varying from 1,500 to 45,500 of their volume. It is well known that carbonic acid gas is formed during germination, and that this decarbonization is necessary to their growth. This action of the air on those parts of vegetables which are not green cannot be considered as a truly vital effect, but as a chemical property inherent in these bodies. Indeed, this action goes on in wood and bark after death; and Rumford has proved by direct experiments, that carbon, which has been considered as one of the most fixed bodies that is known, may become united with oxygen and form carbonic acid gas at a temperature much below that at which carbon will visibly burn. The order of arrangement of this series of composition and decomposition of carbonic acid gas is somewhat obscure. M. De Caudolle proposes the following arrange

ment as the most natural.

1. The water entering vegetables through their roots is charged with carbonic acid, which is carried along with the sap to the green parts where it is decomposed by the solar light; the carbon is fixed, and the oxygen escapes in the form of gas.

2. The carbonic acid gas which those parts of vegetables which are not green have formed with the oxygen of the air, is partly dispersed in the atmosphere, partly dissolved in the water of vegetation, and carried with this water as it is absorbed by the roots, to the leaves, where it is decomposed.

3. The water absorbed by the roots holds in solution a certain quantity of animal or vegetable matter which contains carbon; this carbon is carried by the sap into the green parts; it continues during the night with the oxygen absorbed by them, and in the morning this carbonic acid formed in the leaves, is decomposed by the solar light, as if carbon could not be usefully deposited in the nutricious juices of plants, unless it was formed by the decomposition of carbonic acid.

4. The green parts which are in contact with air or water charged with a small quantity of carbonic acid gas, abstract it, decompose it, and reject the oxygen. If the quantity is more than a twelfth, it acts on the leaf as a poison.

The

2d.

Thus the result of this extensive function, which may be considered as vegetable respiration, is to fix carbon in the plant, whilst the purpose of animal respiration is to diminish the quantity of the same principle. eudiometric influence of vegetable respiration on the atmosphere, may, perhaps, after these considerations, be estimated with some exactness. Living vegetables vitiate the air, 1. Because all those parts which are not green form carbonic acid with their own carbon and the oxygen of the air. Because their green parts absorb during the night a small quantity of oxygen gas. The nitrogen exhaled by the flowers is a temporary and very feeble function, not of sufficient consequence to be taken into account. On the other hand vegetables purify the atmosphere by exhaling during the day a marked quantity of oxygen gas, and at the time of vegetation the days are much longer than the nights. This latter effect is more considerable than the former, for the result of vegetation is to increase the quantity of carbon in a vegetable; now, no molecule of carbon can be fixed there, unless a corresponding quantity of oxygen gas is set free in the air. De Saussure

has confirmed this by experiment. He introduced a small branch covered with leaves and still connected with the tree, into a large round bottle of air, the mouth of which he closed. At the end of two or three weeks the air in the bottle was found to contain a greater quantity of free oxygen than before the experiment.

"Thus, experience as well as theory tends to prove, that living vegetables augment daily the quantity of the free oxygen gas of the atmosphere. This is a compensation for the oxygen absorbed in combustion, in animal respiration, and by dead or dying vegetables. The winds unceasingly mix together every part of the atmosphere, so as to make the whole homogeneous, although in certain places one of these functions may be more active than the other. It is by this mechanism that a fixed quantity of oxygen is maintained in the atmosphere, and thus from the humble functions of vegetable life we are led to the exalted contemplation of the universal order of the world."

This extract will give a general notion of the lucid and complete manner in which M. De Caudolle treats his subject; a subject which has excited, we are sorry to say it, very little general interest in this country. There is some truth in what are called popular prejudices, and unquestionably there is a very common disposition to call in question the advantages of the study of botany. If there are any good reasons for this prejudice, they are derived from the mistaken object for which this study is pursued too often. How many after having collected specimens of every species of plants in their neighbourhood, and having pressed them, neatly pasted them on paper, and written beneath them their Latin names, think that they have accomplished all that their opportunities will allow them, and flatter themselves that they are good botanists. But what have they acquired? A knowledge of the shape of the flowers and leaves, and of the number of the pistils and stamens of a few hundred indigenous plants, the first step perhaps to a knowledge of botany, but no more capable of making a botanist in the philosophical acceptation of the term, than would the study of the words in Walker's Dictionary or a Greek Lexicon be sufficent to make an English or a Greek scholar. A similar error is indeed often made in the study of languages; the acquirement of the language itself being considered the ultimate object, and not the stores of knowledge which such an acquisition may put at the student's disposal. This is, as an acute writer has said, making language not the instrument but the end of instruction; as the negro worships his kettle for its own sake and not for its utility. The simile will well apply to the exclusive admirers of the Linnean system. Dr. Lindley has within the last few years energetically endeavoured both as a writer and a lecturer to dispense with an artificial arrangement of plants altogether, and to substitute the so-called natural one; for he had himself felt the unsatisfactory nature of his acquirements even when he was imagined to be an excellent Linnean botanist. Perhaps he has carried his antipathy to his first master too far to be just, for it is very questionable whether any artificial adaptation of the natural system will be equal as an index to that of Linneus; for it must be recollected that however natural the Natural system may be, yet that an artificial division must be appended in order to save the time of the learner in ascertaining the names of those families with which he is unacquainted. But although it might be inconvenient to do away with

the Linnean arrangement as an Index, it is not to be regretted, that Mr. Lindley, in his ardour for the promulgation of a more scientific one, has gone to extreme lengths, for he is more likely by such means to excite attention to the true object of artificial classification, and thus to induce more extensive investigations. One of the great benefits of the Natural system is, that its primary divisions are founded on internal structure, and therefore there is a greater probability of its leading the student to inquire into the anatomy and physiology of plants, so as to give a somewhat philosophical character to his investigations, and thus to raise botany in the general opinion to that high rank in the sciences which it undoubtedly should hold. The excellent introduction to Botany of Dr. Lindley, and the translations of Richard's Elémens de Botanique, will do much to accomplish the same purpose, and those who are disposed to enter more deeply into the study of the structure and functions of plants will find in these volumes of M. De Caudolle, and in those which have preceded them, a fund of matter as valuable and as well arranged as was ever brought together to elucidate any similar subject.

AN INQUIRY INTO THE NATURE OF SLEEP AND DEATH, WITH A VIEW TO ASCERTAIN THE MORE IMMEDIATE CAUSES OF DEATH, AND THE BETTER REGULATION OF THE MEANS OF OBVIATING THEM; BEING THE CONCLUDING PART OF THE AUTHOR'S EXPERIMENTAL INQUIRY INTO THE LAWS OF THE VITAL FUNCTIONS. (Republished from the Philosophical Transactions.) By A. P. W. Philip, M.D. &c. &c. 8vo. pp. 254.

OUR first glance over the title-page of this volume engendered a hope that Dr. Philip had discovered some means of baffling the grim tyrant Death, by depriving him of the weapons by which he cuts down man at all periods of existence. A more close examination, both of the title and the body of the work, has lessened our hopes, and left us in possession of the facts, that diseases and even disorders of the vital organs and functions, carry us off before the age of three score years and ten-and that, even if we are fortunate enough to escape sickness, TIME itself will moulder us into dust after that epoch! If ever man deserved immortality, Dr. Philip is that man; for he has studied the "laws of the vital functions," till, we should imagine, he has them all by heart. But if our worthy and indefatigable author has not been able by any experiments on animals, to secure himself from the grave, he has done enough to transmit his name and his fame to posterity-(which is all that the most talented can do, or the most ambitious expect)-and that too notwithstanding the Ulyssean stratagems of Prout, or the Ajax-like lounges of Earle against the "laws" laid down by Dr. Philip.

As most of the papers in this volume have been long before the public, it is not our intention to notice more than the last two chapters, on sleep and death. Nor shall we go very minutely into these. The former subject is a drowsy, and the latter is a melancholy one. Most people indeed, would

rather enjoy the refreshment of a sound sleep, than listen to the most philosophical discussion on its nature and causes. However, as physicians and philosophers must have many sleepless hours, they may as well amuse themselves with a discussion on this, as on any other subject. Dr. Philip's long dissertation on sleep may be brought into a very narrow compass. There is no organ or structure in the body, neither heart, arteries, muscles, or glands, that can carry on uninterrupted action-Dr. Philip to the contrary notwithstanding-and, therefore, the sensorial functions require their period of rest, as well as those of the stomach or any other part. The brain is tired during the day, by the reception of sensations and the exertion of reflections, volitions, &c. and at night we sleep. Dr. Philip maintains that the arteries are in perpetual action. We deny it, nor would a thousand experiments on frogs or rabbits convince us of this perpetuity. Dr. Philip admits that the heart appears to have a periodical relaxation, and cessation of its proper stimulus, the blood. Now the heart is never free from the presence of blood, as Dr. Philip must know. The ventricle never empties itself entirely. But as the systole occupies only about a third part of the time occupied by the diastole, it follows that the muscular fibres of the heart are sixteen out of the twenty-four hours in a state of inaction. This is about the period of rest which is enjoyed by the voluntary muscles. The same argument applies to the arteries. If we recollect right, Dr. Philip maintained, in opposition to Dr. Parry, that the arteries contracted and dilated like the heart, though in different rhythms. If this be the case, they have their alternations of labour and repose, like other muscular structures. The muscles of respiration, we need not say, have the same proportions of rest. Even the secreting organs, as the liver and kidneys, which appear to be more perpetually in action than almost any other parts of the human frame have, in reality, alternate labour and repose. Secretion may never, perhaps, entirely cease; but it is periodically in activity and inactivity, comparatively, which answers the same purpose. As to the veins, it will not be said that they are in perpetual action. During the greater part of their time, they are merely passive hydraulic machines, or tubes to convey the blood from one part to another.

Dr. Philip maintains that that part of the brain which supplies nervous energy to the vital organs, as the heart, arteries, &c. is in a state of perpetual or uniform excitement. This may be so; but, if we are correct in shewing that the functions of these organs are in alternate action and repose, we do not see why the brain itself should not be similarly situated? We shall give Dr. Philip's conclusions, however, in his own words, as containing the pith of the paper.

"From a review of the whole of the facts which have been laid before the Society, it appears,

1. That in the brain and spinal marrow alone reside the active parts of the nervous system.

2. That the law of excitement in the parts of these organs, which are associated with the nerves of sensation and voluntary motion, is uniform excitement followed by proportional exhaustion, which, when it takes place to such a degree as to suspend their usual functions, constitutes sleep; all degrees of exhaustion which do not extend beyond them and the parts associated with them, being consistent with health.

3. That the law of excitement in those parts of the brain and spinal marrow

which are associated with the vital nerves is also uniform excitement, but which is only, when excessive, followed by any degree of exhaustion, no degree of which is consistent with health.

4. That the vital, in no degree partaking of the exhaustion of the sensitive system in sleep, only appears to do so from the influence of the latter on the function of respiration, the only vital function in which these systems co-operate, in consequence of which its organs, without being in any degree debilitated, are less readily excited.

5. That the law of excitement of the muscular fibre, with which both the vital and sensitive parts of the brain and spinal marrow are associated, is interrupted excitement, which, like the excitement of the vital parts of these organs, is only, when excessive, followed by any degree of exhaustion. And

6. That the nature of the muscular fibre is every where the same, the apparent differences in the nature of the muscles of voluntary and involuntary motion depending on the differences of their functions, of their relation to the brain and spinal marrow, and of the circumstances in which they are placed." 150.

Dr. Philip has appended some observations on dreaming, which have nothing particularly novel in them. Although the sensorial powers of the brain become so exhausted that sleep ensues, it does not follow that they are so completely exhausted as not to receive impressions, though indistinctly. It is these faint impressions, from within or without, that cause dreaming. These causes are chiefly from irritation in the digestive organs, as every one who has eaten a heavy supper-or who has weak powers of digestion, must well know. The silence and quietude that generally prevail during sleep tends, also, to promote the perception of sensations then, which otherwise would pass unheeded even when we are wide awake, and when the mind is employed in the avocations of the day. The rapidity of the operations of the memory and imagination, during sleep and in the act of dreaming, is most curious and unaccountable, and so are the incongruities which then occur, and which appear perfectly natural and correct to the dreamer. Philip endeavours to explain these phenomena in the following manner, but with what success we shall not decide.

Dr.

"It seems greatly to influence the phenomena of dreaming, that in order to favour the occurrence of sleep, and thus as far as we can prevent unnecessary exhaustion, means are always employed at its accustomed times, to prevent, as much as possible, the excitement of the external organs of senses, and consequently those parts of the brain associated with them. This renders us the more sensible to causes of excitement existing within our own bodies, while, by the inactivity of the parts of the brain which are associated with those organs, we are deprived of the usual control over such parts of the mental functions as are thus excited; the effect of which is greatly increased by the rapidity of the operations of the memory and imagination, when not restrained by some of the various means employed for that purpose in our waking hours. These are often objects of the senses, as written language, diagrams, sounds, and sometimes even objects of touch; but the most common is the mere use of words, independently of any object presented to our senses.

Any one may easily perceive how difficult it is to pursue a train of reasoning without this means of detaining his ideas for the purpose of steadily considering them and comparing them together. Now, in sleep, in consequence of the excitement of the brain being so partial, we are deprived of all these means; and our ideas pass with such rapidity as precludes all consideration and comparison Our conceptions, therefore, are uncorrected by experience, and we are not at all VOL. XXI. No. 42.

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