DR. CARPENTER'S ANIMAL PHYSIOLOGY.
Tan object of this volume, forming part of the Popular Cyclopmdia of Natural Science, is to furnish "an elementary treatise on animal physiology to those who desire to gain a general acquaintance with the science, or who are entering upon the professional study of it." The plan of Dr. CARPENTER'S work is founded upon that of M. Mmen-EDWARDS'S Anatomic et Physiologic, which is adopted as the text-book of instruction in the colleges connected with the University of Paris. The execution of Dr. CARPENTER'S book, however, is very different. In the first place, it is twice the size ; which admits the introduction of a large amount of additional matter. In the second place it exhibits more of the general prin- ciples of the subject than the French prototype ; Dr. CARPENTER not only tells what is, but why it is so. The plan is rather synthetical than analytical ; but, when per- ceived, is well adapted to convey a clear and comprehensive idea of the subject. After a general introduction, on the vital opera- tions of animals and the instruments by which they are performed, Dr. CARPENTER gives an account of the structure of the primary tissues, or elements of animal matter, as far as chemistry has yet reduced them, and then of the four classes into which all animal life is divided. Food is next considered, first as regards the ele- ments into which it may be resolved, and then in its digestion and absorption. Blood and its circulation are then examined ; being shown, like digestion and absorption, through the different classes of animals. The other functions follow—as respiration, secretion ; after which, the nervous system, and its effects in producing in- stinctive actions and sensations, are handled; and lastly, animal motion, the voice, instinct, and intelligence.
The book is, of course, a compilation, even in such parts as are not drawn direct from MiLsie-Enweans; but it is the compilation of an able man, who has given a professional attention to the subject he is treating, and is competently skilled in the art of writing. The book is full of matter ; every thing is distinct in ar- rangement, and clear in expression ; the later discoveries in animal chemistry are set forth according to their probable truth ; and the examples selected to exhibit the principles are well chosen from the most curious instances of the animal creation. Something of heaviness is perhaps inseparable from a subject requiring a constant stretch of the attention : but this will be diminished if the nature of the plan be borne in mind,—that the exposition begins with the tissues or elements of which all living bodies consist, next proceeds to consider the classes into which all animals are divided, then to the food whence they derive their support, and afterwards exhibits their structure and functions.
Let it be remembered that the book is an exposition of phy-
Biology, not an account of disease or an art of preserving health ; though some general remarks on these subjects are found in the introduction, and some scattered passages on the animal economy will furnish hints for general management. Here are some
FACTS ON BUTTER AND CREESE.
The mixture of the azotised and non-azotised compounds (gluten and starch) that exists in wheat-flour, seems to be juet that which is most useful to man; and hence we see the explantion of the fact, that, from very early ogee, bread has been regarded as the " staff of life." In regard to the nutritious properties of slifferent articles of vegetab'e food. these may be generally measured by the proportion of azote they contaiu, which is in almost every Instance less than that which exists in good wheat-flour. But it must not be forgotten that, owing to the varieties of constitution which have been pointed out among dif- ferent animals, the power of particular substances to nourish man and cattle is not the same—the latter requiring a larger proportion of the saccharine and oleaginous compounds, than is beneficial to him—especially when it is an object to cause a large quantity of fatty matter to be deposited in their tissues, or to be excreted in milk. Thus, potatoes are found to increase the proportion of butter in the milk of a cow that feeds upon them ; their starch being probably converted into fatty matter. It has been also shown by recent experiments, that the proportion of butter in the milk of a cow allowed to feed during the day in a pasture, and shut up at night in a warm stall, was much greater in the morning milk than in the evening—the former containing 5.6 parts of butter in 100, and the latter only 3-7 parts. This was evidently due to the diminished demand for the materials for respiration during the night, when the body was at rest and the skin kept warm. The experiment was then tried of keeping the cow in a shed during the day, and feeding her with the same grass ; and the proportion of butter in her evening milk then rose to 5-1 parts in 100. But this plan diminished the proportion of casein or cheesy matter in the milk; which was increased again by allowing the cow to pasture in the open field. Hence it appears, that stall-feeding is most favourable to the production of but- ter, and pasturing to that of cheese.
The following interesting sketch of the power exerted by birds in their flight, and the demonstration of man's incapability of flying, is from the chapter on Motion.
"The degree in which the wings act in raising the body, or in propelling it through the air, varies considerably in different animals, according to the way in which they are set. Thus, in birds of prey, which require a rapid horizontal motion, the surface of the wings is very oblique, so that they strike backwards as well as downs ards, and thus impel the body forwards whilst sustaining it in the air. Such birds dud a difficulty in rising perpendicularly; and can in fact only do so by flying against the wind, which then acts upon the inclined sur- face of the wings just as it does upon that of a kite. On the other band, the lark, quail, and such other birds as rise to great heights in a direction nearly vertical, have the wings so disposed as to strike almost directly downwards. It has been estimated that a swallow, when simply sustaining itself in the air, is obliged to use as much force to prevent its fall, as would raise its own weight to a height of about twenty-six feet in a second. Hence, we may form some idea of the enormous expenditure of force which must take place when the body is not only supported but raised and propelled through the air. The eider. duck is said to fly ninety miles in an hour, and the hawk one hundred and fifty. The swallow and swift pass nearly the whole of the long summer days upon the wing, in search of food for themselves and their helpless offspring; and the rapidity of their flight is such that they can scarcely traverse less than seven or eight hundred miles in that time, although they go but a short dis- tance from home. The flight of insects is even more remarkable for its velo- city in proportion to their size : thus a swallow, which is one of the swiftest- flying of the birds, has been seen to chase a dragon-fly for some time without success; the insect always keeping about six feet in advance of the bird, and turning to one side and the other so instantaneously, that the swallow, with all its powers of flight and tact in chasing insects, was unable to capture it. "If the preceding estimate of the power expended by a bird in sustaining itself in the air be correct, it may be easily proved that it would be impossible for a man to sustain himself in the air, by means of his muscular strength alone, in any manner that he is capable of applying it. It is calculated that a man of ordinary strength can raise 13* pounds to a height of ai feet per se- cond, and can continue this exertion for eight hours in the day. He will then exerta force capable of raising (13*X 60 X60 X8) 381,600 pounds to a height of ai feet ; or one-eighth that amount, namely 47,700 pounds, to the height of 26 feet, —which, as we have seen, is that to which the bird would raise itself in one second by the force it is obliged to exert in order to sustain itself in the
air. Now if we suppose it possible, that a man could by any means concentrate the whole muscular power required for such a day's labour into as short a period as the accomplishment of this object requires, we might find the time during which it would support him in the air, by simply dividing this amount by his weight, which we may take to be 150 pounds. The quotient is 318, which is the number of seconds during which the expenditure of a force that would raise 47,700 pounds to a height of twenty-six feet will keep his body supported in Omsk ; and this is but little more than five minutes. There is no possible means, however, by which a man could thus concentrate the force of eight hours' labour into the short interval in which he would have to expand it when supporting himself in the air. And we have elsewhere seen (Mechanics, §. 285,) that by no combi- nation of mechanical powers can force be created ; as these only enable force to
be more advantageously applied. Hence, the problem of human flight will never be solved, until some source of power shall be discovered far surpassing that which his muscular strength affords, and so portable in its nature as not materially to add to his weight."
The volume is illustrated by a profusion of wood-cuts; some- times merely presenting a thing to the eye—as an animal that happens to be mentioned, but more frequently serving to explain the anatomical descriptions of the text, and occasionally com- bining both features.
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