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The water grows hotter and hotter, but the brainless frog never moves, till, at 56° C, it expires in a state of tetanus. This contrast is assuredly marked enough, and most readers will be disposed to admit that if the brainless animal can endure, without manifesting even uneasiness, what in the normal animal produces every sign of intense pain, the conclusion that the brainless animal feels nothing, and therefore that his Spinal Chord is not a sensational centre, is irresistible. This conclusion I altogether reject. Not that I question the facts, for I have verified their accuracy; and Mr. Foster, who has repeatedly verified them, only points to the new difficulty which they raise, namely, why the brainless frog is not excited to reflex action by the stimulus of hot water? It is, therefore, the interpretation of the facts to which attention must be drawn; and to make this complete, let me here note counter facts which my experiments presented.

The brainless frog is not insensible to the heat, unless the insensibility be gradually produced. If its foot be dipped into the hot water the leg is violently retracted; and if the whole or greater part of the body be immersed, the frog struggles vehemently, and rapidly passes into a state of tetanus. The difference between the behaviour of a normal frog and a brainless frog when suddenly immersed in very hot water is not greater than might reasonably be anticipated between animals uninjured and animals with one great sensitive centre removed.

These facts are substantially confirmed by the facts brought forward in Mr. Foster's paper. He also finds the legs of a decapitated frog withdrawn by reflex action, as soon as the temperature of the water reaches a little over 300 C. "However slowly the water be heated, the feet are always withdrawn at a temperature of 350 or earlier." But he observes that when the whole body is immersed and the water gradually heated, no movement, or only the very slightest spasm of the muscles of the legs takes place. The point to which he draws attention is, that whereas the stimulus of hot water applied to the foot causes reflex action, applied to the whole leg or the whole body it causes none; his explanation is that the depressing influence of heat on the Spinal Cord destroys its reflex powers. This explanation seems to accord very well with all his observations, but is not in accordance with the fact mentioned by Goltz of the frog's wiping away the acid which is dropped on its back; a fact clearly manifesting the presence of reflex sensibility.

It is this fact which I should urge against Goltz, and all who share his views. It proves, to my mind, that although the frog remains motionless in the heated water and shows no sign of pain from the stimulus of heat, this is assuredly not because Sensibility in general is gone, but simply because Sensibility to temperature is gone. It is not necessary to refer to the many well-authenticated cases of analgesia without anaesthesia, of insensibility to pain or temperature without insensibility to touch ; 1 will parallel Goltz's case of the brainless frog suffering itself to be boiled without moving, by the case of the frog with its brain and other nerve centres intact, allowing its legs to be burnt to a cinder without moving. In a paper read at the Aberdeen Meeting of the British Association, I brought forward some experiments on frogs after their skins had been wholly or partially removed. (There were small patches of skin left on the head wherewith to compare the effects of stimuli). These frogs assuredly had not lost their Sensibility; they responded, as usual, to any stimulus applied to the patches of skin which remained; and as these responses were the responses of animals in possession of a brain, no one would explain them away as mere reflexes. Yet these sensitive frogs allowed their flayed limbs to be pinched, pricked, cut, burnt with acids, and even burnt to a cinder with the flame of a wax taper, yet remained motionless under all these stimuli, though a touch on the patch of skin would make them wince or hop away.

I did not try the experiment of boiling one of these frogs, but who can deny that the insensibility they presented with their brains and without their skins, is even greater than that presented by brainless frogs with their skins? The point urged is that the frog without its brain is incapable of feeling the stimulus of hot water, which, when the brain is intact, is felt intensely; and the conclusion drawn is that the spinal cord is not a sensational centre. But this point is blunted when we find that the frog is equally insensible to the heat, when its brain is intact and only the skin removed. Ought we to conclude that tbe skin is the sensational centre? The one conclusion would be as logical as the other.

Mr. Foster, who is only treating of the influence of temperature, asks why the sensations and centra! processes are not dulled in the same way as he supposes the spinal processes to be dulled by heat ?" The answer,'' he says, " is that a less intense sensory impulse is needed to call forth a movement of volition, that is, a movement carried out by the encephalon, than an ordinary reflex action, that is, a movement carried out by the spinal cord alone. The water as it is being warmed suggests a movement to the intelligent frog long before it is able to call forth an unintelligent reflex action. The very first movement of the frog, the removal of any part of his body out of the water, increases the effect of the stimulus ; for the return of the limb to the water already warm gives rise to a stronger stimulus than contact with the water raised to the same temperature while the limb is still in it; and thus one movement leads to another and the frog speedily becomes violent. It is nearly the same with the brainless frog when a movement has for some reason or other been started; only in the observations we have been dealing with this initial movement is wanting."

Let us compare the energetic movements of the normal frog and the absence of movement in the brainless frog, with the energetic movements of a waking man in a suffocating atmosphere, and the absence of movements in the sleeping or stupefied man in the same atmosphere, and all the phenomena are clear. The waking man and normal frog are alert and alarmed. The sleeping man and brainless frog remain motionless. Instead of our being surprised at the brainless frog manifesting so little Sensibility when the gradually-increasing heat is threatening its existence, we ought to be surprised at its manifesting so much Sensibility as a thousand experiments disclose; especially when we see that if the heat be suddenly applied the Sensibility is manifested as equally energetic in normal and in mutilated frogs.

In conclusion, let it be observed that unnecessary obstacles are thrown in the way of rational interpretation when connotative terms such as Spinal Soul {Riickenmarkseele) are adopted. It is one thing to assign a general physiological Property, such as Sensibility, to the nervous centres; another thing to assign a term which is the abstract expression of the connexus of sensibilities, to any one centre. In saying that the Spinal Cord is a seat of sensation, it is not meant that it is the seat, nor that the sensations are specifically like the sensations of colour, of sound, of taste, of smell ; but they are as like these as each of these is like the other.

George Henry Lewes

THE ARTISTIC REPRESENTATION OF NATURE*

""PHE late autumn of every year introduces to the public -1 a large supply of gorgeous volumes, "/got-up" in lavish fashion with handsome plates and lightly-written letter-press, which are generally spoken of as Christmas Books, and are intended to be the means for the material expression of the generous feelings which that season is

* "The Life and Habiti of Wild Animals," Illustrated by Desiims by J. Wolf. (Macmillan, 1873.) *'

supposed to evoke. The work to which we wish to call attention is not intended to be one of these, though its exterior appearance might, at first sight, be thought to warrant the supposition. It is a special work brought out under special circumstances, and, as we are told in the preface, the plates have been engraved for nearly seven years. We refer to it, and shall speak of some of the pictures in detail, as showing the service which Art can render to Science by a faithful representation of Nature. The more scientific Art is, the more successful and themore impressive she will be; only by a thoroughly scientific study of his subject and its surroundings can an artist hope to achieve complete success.

The book derives a special, though a painful interest, from the fact that it contains the last series of illustrations which will be drawn by a highly-talented German artist—Mr. Wolf—the previous productionsof whose penc:l are so well known to all who find pleasure in the'study of the animal world. The volume is illustrated by twenty plates, beautifully engraved by Messrs. J. W. and E. Whympcr, each of which depicts some stirring scene in the life of "our four-footed friends," or puts before us some picture of the life of birds, some of them representing in a terribly graphic manner the struggles which pervade the existence of beasts, and render its tenure so precarious. Witness the subject of plate iii.— one of the most powerful in the whole series—the deathgrip of the crocodile's cruel jaws upon the handsome head of the tiger drawn slowly and resistingly beneath the stream where the conqueror will make his banquet. There is no one who would not feel, in gazing at this picture, a strong sympathy with that most splendid of the feline tribe in this his death-agony. We do not select this plate as superior in draughtmansbip to its fellows; they are all of the same high order of merit, though some naturally arrest the attention more forcibly than others, in proportion as the feelings which connect man qud animal with his fellow-animals find fuller expression with regard to the nobler and higher specimens of animal life.

And here we would say that pictures like these—not mere passive delineations of the outward shapes, but illustrations of the habits of wild animals—have an instructive and suggestive value. They are pictures which set one thinking. There is a dramatic reality about them which leads the mind into the by-paths of contemplation as no still outline can—they irresistibly compel us to compare with ourselves these denizens of the forest and the prairie, of the river and the sea. We seem at once to be impressed with the consciousness of their irresponsibility, of their independence of ethical restraints, obeying as they do but one law—the law of their kind—which , incidentally leads them to the destruction of other kinds I inferior to their own. The half-human looking ape does' not allow us to predicate the conception of morality of any of its actions ; the care of its young which it evinces is but an exhibition of the instinct of self-preservation which pervades all species of the higher animal forms; it is difficult to realise that the gap between man and monkey is anything less than a so-called difference of kind. Many | other reflections are suggested by a sympathetic survey of such animated drawings as these, but we will not weary our readers with subjective digressions, which must neces- I sanly vary with the individuals who indulge in these | reflections; we are only eager to impress the superiority' in this regard of delineations of active life and habits over mere portraiture, however well executed, of indi-' vidua! forms ot life.

We are glad to be able to reproduce one of the most pleasing of the plates which adorn Mr. Wolfs work—" The Island Sanctuary." There is a peaceful lonely beauty about this representation of the osprey's haunt, which at once arrests the attention and forms a strong contrast with the depictions of the more savage warfare of species against species, of panther j

against doe, of lion against deer, of wolf against boar, which are contained in the same volume with it The siesta of the jaguar (plate ix.) and the bath of the large pachyderms, elephants and hippopotami (plate x.), are two of the most striking drawings in this volume, the former especially we think inimitably excellent. There is an idyllic completeness in the representation of the largest of the American cats taking its ease during the midday heat on the branches which overhang the river. Without going into further detail concerning the separate plates, which require to be seen to be appreciated, we would mention one more, Catching a Tartar (plate xviii.), the most sensational in the series, very forcibly drawn, the dead or dying owl's wings have lost their motive power, but in their outstretched hugeness serve to break the rapidity of the descent and save the weasel, whose "cunning has proved more than a match for the strength of the more powerful" bird.

We speak in a somewhat popular strain of Mr. Wolf's work, not with any intention of treating it as one of the hastily concocted products of the winter season, which, as we have said, it is not meant to be, but rather from a belief that it will appeal to those who, without a special scientific or zoological training, have vet a genuine love of contemplating the varied phases of life in beast and bird, who believe with Coleridge, that

"He prayeth well who loveth well Both man and bird and beast," and to such as these we can say that this volume is of no common sort; the pictures are such as stir the imagination and please the taste, while, as justly remarked by Mr. Whymper in his preface, their value is greatly enhanced by the " power of delineating specific characters" which is displayed.

We must not omit to mention, in connection with Mr. Wolfs plates, the letterpress which accompanies them, and which is from the pen of Mr. Daniel G. Elliot, of the United States. It is, of course, in this case subservient to the drawings which it interprets. In bis outspoken preface, to which we have already referred, Mr. Whymper tells us that Mr. Elliot has laid aside the scientific treatment of his subject, for which he is fully capable, as bearing in mind that " the book is intended for the general public, and not for a class." Our American cousins are always masters of the art of depicting in animated and picturesque fashion all that is of interest in life and action, whether in man or in beast; and Mr. Elliot has not failed in the task set before him ; he has steered clear of fulsomeness, and cannot be accused of padding; his writing is instructive with respect to the habits of animals, and is not of that ejaculatory kind which too often accompanies pictures and seeks to impress the character of eloquence by a copious interlarding of interjections. We can give in one quotation a fair example of his portion of the work. Speaking of the gorilla he says :—" In the pathless tracts of those ancient woods, distant even from the primitive abodes of hardly less savage men, in company with the fierce inmates of the jungle, the gorilla dwells, surrounded by his family. Peacefully they pass the day, seeking the various fruits that in many a cluster hang from the lofty trees, paying generally but little attention to what is passing below them. But if any unusual sound breaks the stillness of the wo jds, or a strange form be seen approaching their vicinity, then the females, bearing their young clinging fast to them, flee away into the still deeper recesses of the forest; while the lather and protector of the small community, swinging himself rapidly from tree to tree, tearing loose the vines that stretch across his passing form, advances towards the object of their fears, and before imitating the rest in their speedy flight, satisfies himself in regard to its presence, and then with many a hideous grimace, and short hoarse call, demands to know, in impatient tone, Who comes here?"

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ON THE SCIENCE OF WEIGHING AND
MEASURING, AND THE STANDARDS OF
WEIGHT AND MEASURE*
IX.

IN the comparison of standard weights, the difficulty and risk of error in determining the weight of air displaced by them is to be avoided by weighing them not in air, but in a vacuum. Two methods are employed for this kind of weighing.

In the first and simplest method, when an ordinary balance of precision is used, each standard weight is placed in an exhausted receiver just large enough to hold

it, and is weighed separately against a counterpoise by Borda's method. Sensible discordances have, however, been found in the results of this method of weighing in exhausted receivers, which render its use inexpedient when scientific accuracy is required. These discordances are perhaps attributable to a small quantity of air being present in the receiver during the weighings, the amount of which cannot be accurately determined. Another probable cause is a change in the temperature and atmospheric pressure affecting the balance itself and the weights in the pans during the long time necessarily occupied in the whole process of this method of weighing. Indeed it may be generally stated as a rule that the risk of discordances in the results of weighings is in proportion

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to the time occupied in the operation. Such discordances are not found when the weighings are made by the second method, when a vacuum balance is used, that is to say, when the balance case itself is made an exhausted receiver.

A vacuum balance has been constructed at Paris by M. Deleuil, and is now used at the Conservatoire des Arts et Metiers, consisting of a balance of the best construction placed in a very strong cast-iron case that can be made perfectly air-tight. This case has four circular openings for giving admittance and light to the inside, which are closed with strong glass covers. It has a

• Continued from p. 49.

stuffing box for the handle of the lever by which the balance is put in action and arrested. This balance has been found to give very accurate results of weighing in a vacuum. But the comparison of standard weights in this vacuum balance takes a considerable time from the necessity of opening the case and re-establishing a va cu.im at least a second time in order to change the weights in the pans even when Borda's method is used; and occasionally this must be done again if a small additional balance weight is required to be placed in either pan, in order to obtain a sufficiently approximate equilibrium, so that the pointer may not exceed the limits of the index scale.

Some improvements on Deleuil's vacuum balance have been designed by Prof. W. H. Miller, and have been practically carried out in a vacuum balance constructed by Mr. Oertling for the Standards Department. The balance case consists of a strong brass frame cast in one piece, with a rectangular base, two sides, and an arched top. Two solid glass plates, each 1^ in. thick, form the front and back of the case, being clamped to plane surfaces of the brass frame, and made air-tight by interposing thin india-rubber. They are thus removable when required, for instance, when any al'eration is needed in the balance. There is a circular opening 4;; in. in diameter, on each side of the brass frame, similar to those on Deleuil's balance, to which glass covers are fitted. There is no stuffing-box, but when the Standard weights to be compared arc placed in the pans, and the balance case exhausted, contrivances are arranged for putting the balance in action and arresting it, for adding any balance weights to either pan and removing them, and for interchanging the pans and weights by transferring them to the other end of the beam, without any disturbance of the vacuum, or necessity of opening the case.

These arrangements enable the weighings to be made by Gauss's method of alternation. The balance case is firmly placed upon a strong mahogany stand. Two iron tubes are fixed underneath and opening into the balance case. They rest in iron cups containing a sufficient quantity of mercury. Within each tube is a steel rod rising to the required height inside the balance case, and having at the top an arm ot convenient form. By means of a simple lever handle outside the tube, either rod can be lifted about an inch, and it can also be turned round. By this rotary motion, when the left-hand rod is in its normal position, it acts upon two bevelled wheels, and thus lowers the supporting fnune of the beam and puts the balance in action ; and by reversing the motion, the action is stopped. By raising either rod to nearly its full height, it can be made to take up one of several small balance weights riding on a little rail fixed to the pillar of the balance, and transfer it to a similar rail at the top of the pan, or to transfer it back again. Again by raising either steel rod to an intermediate height, and turning its arm under the arched rods of one of the pans, and then raising it a little, the pan and weight can be lifted off the hook of the beam and transposed to a small carriage standing upon a railroad near and parallel to the front of the balance-case. In a similar way the other pan and weight can be transferred to a second carriage at the back of the case. By means of a cord and pulleys, one of which is upon the right-hand steel rod and can thus be turned round with the hand, the two carriages can be moved to the other ends of the case, and then each pan with its weight can be attached to the hook at the other end of the beam. The desired results are all thus attained, and the whole action of the balance is open to view.

The construction of this new vacuum balance may be seen from Fig. 19.

The balance itself is similar in construction to the other Standard balances made by Mr. Oertling. It is constructed to weigh a kilogram in each pan. There are two Standard thermometers inside the case, one fixed to each pillar, and adjustible as to height, so that its bulb may be on the same level as the centre of gravity of the weight. A mercurial gauge is fixed between the pillars, and there is the same arrangement of three tubes and stopcocks communicating with air-pumps and with a mano-barometer, as in Di leuil's vacuum balance. Two glass vessels containing chloride of calcium, are also introduced for absorbing any moisture in the balance case.

There are two ways of comparing and verifying standard measures of capacity. The first and most accurate, as well as scientific method, is by weighing their contents of distilled water; the second method, which is simpler and

more ordinarily used, consists in comparing the measure of water contained in them, with the contents of a verified standard measure.

In weighing the contents of distilled water contained in a standard measure, when quite full to the brim, and with the surface of the water made accurately level by a disc of plate glass slid over it, Borda's method of weighing is employed. The measure with its disc is placed empty in one of the pans of the balance, and is accurately counterpoised. A verified standard weight equal to the legal weight of water contained in the measure is then added to the pan containing the measure and disc, and is accurately counterpoised, and a sufficient number of weighings is taken until the mean resting-point of the balance is determined and noted. The standard weight is then removed. The measure is exactly tilled with distilled water, and its temperature, together with the reading of the barometer noted. Any difference in the actual temperature and barometric pressure from the normal temperature and pressure is to be compensated by equivalent weights placed either in the measure pan or weight pan as required. If an equipoise is not now obtained, additional weights are placed in the pin until an equilibrium is produced, and any difference from the normal correcting weight for temperature and barometric pressure

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Fig. 20.—Field of Micrometer of Microscope.

either plus or minus, shows the error of the measure in relation to its legal weight of water at the standard temperature and barometric pressure.

For ascertaining the exact amount of the proper corrections for temperature and barometric pressure, authoritative tables are computed both for Imperial and for Metric Measures. Such tables will be found in the Papers appended to the Fifth Report of the Standards Commission, published in 1871 (pp. 81, 193, and 196), and to the Sixth Annual Report of the Warden of the Standards, published in 1872 (pp. 49 and 51).

With regard to comparing instruments for standard measures of length, their construction has necessarily varied according to the form of the standard measure. As has been already stated, the earlier scientific standards of length were defined by two points, and all comparisons were made by means of a beam compass.

The introduction by Mr. Troughton of the use of the micrometer microscope was a great step in advance towards the attainment of scientific accuracy in the comparison of our standard measures of length. It enabled optical observations to be made without injurious contact to the defining points or lines, and thus without interference with the permanence of the

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