physiologists, in the strict sense, than the navigator is called upon to be an astronomer. Hence you may converse with medical men of high position and find them not only unacquainted with the great physiological discoveries of modern times,* but also betraying very vague knowledge even of the old physiology; but if a new method of cure, or a new mode of operating, be mentioned, you will find them perfectly familiar with it, because this concerns their art, and not to know this would be disgraceful to them. They practise an Art, they do not prosecute a Science; they have to cure an individual patient of a particular ailment, not to discover the general laws of organized beings. Their practice will of course be guided by the scientific doctrines reigning in their day, aided by empirical knowledge and traditional precept; and in as far as their practice is guided by sound theory it will be successful.

The intimate relation subsisting between theory and practice, physiology and medicine, has been somewhat masked by the indispensable presence of empirical precepts -indispensable we say, while theory is perfecting itself: for physicians cannot afford to await the slow elaboration of science when the patient is suffering; while the grass grows the proverb is somewhat musty. In consequence of this necessary adjunct of empiricism men have been apt to overlook the importance of theory. If they overlooked the importance of Physiology what wonder that they overlooked the importance of Comparative Anatomy, the bearings of which are still more remote? John Hunter was sneered at by his brethren for bothering himself about flies and frogs; no one dreaming that Hunter's researches in comparative anatomy were destined to modify the prescriptions' of Hunter's successors. Nor is it wonderful that men should fail to see bearings so remote as

those of abstract science upon a special art. To Englishmen of the Revolution, feverish with anxiety respecting the fate of James, on whose conduct the world seemed to depend, it would doubtless have appeared very preposterous if some mathematician, intensely interested in the newly discovered differential calculus, had suddenly exclaimed:

This question of the calculus is infinitely more important to you and to the world than the fate of all the dynasties of Europe! Yet now we see that the mathematician would have spoken truly.

We seem to be digressing, but only seem. Our subject is the greatest comparative anatomist of the age, and it is necessary we should indicate, however briefly, the office which Comparative Anatomy has to perform. To any one who has ever dabbled in the fascinating speculations, now becoming fashionable, which are connected with the Science of Life, the necessary importance, and the exhaustless interest of Comparative Anatomy will need no advocate. Quite apart from the marvels of organization which it reveals, we may assert that only by its aid can we hope to gain insight into the simplest problems of life. Let us see this illustrated in an example or two.

Is bile a secretion or an excretion? Is it formed from the blood, by the conversion of materials in the blood; or does it exist, as a product of disintegration of tissue, ready formed in the blood, like urea? Is it formed in the liver, or only filtered by the liver from the blood? This question, thus variously asked, is of immense importance. To answer it was not easy. Moleschott, however, removed the liver from frogs; during several months he examined their blood, and found in it no trace of bile; the conclusion was irresistible: bile is a secretion formed by the liver from materials furnished in the blood.+

coveries, and we crown certain men, as if the honour were solely theirs. In the present day there is no work with which to compare Owen's Lectures, except the classical work of Siebold. Owen has the superiority of philosophical grasp, which gives life and purpose to otherwise dry details.

Vast as his knowledge is, careful as his mind is, Owen of course is not infallible. Probably no man has dissected so many animals, and to such purpose; yet it is certain that his industry has not carried the scalpel into every corner of every organism described by him. The consequence of this may be foreseen the learned Brown, who has spent years in the dissection of cockchafers, and the distinguished Jones, who has devoted the energies of a life, sir,' watching the development of sandhoppers, will express themselves with great scorn on finding that Owen has omitted to state the number of muscles in the cockchafer's thigh (or perhaps stated them inaccurately), and failed to record all the embryotic changes of the interesting Talitrus. To these learned gentlemen will be added the great compiler, Smith, who engaged in the easier task of reading foreign journals, while Owen has been making dissections, will point out with many chuckles that several of the newest contributions to those journals have not been mentioned by the professor. In short, the work is not unapproachable from the trenches of criticism; but whatever lynx-eyed eagerness may discover in it, he is a bold man who will look down upon it from the height of his mole-hill. We cannot here attempt a detailed criticism of such a work, but we may earn the gratitude of philosophic readers by directing their attention to it.

Our remarks may fitly begin with the beginning-namely, the old vexed question of the difference between Plants and Animals. 'In entering upon a description of the animal kingdom, the naturalist's first and greatest difficulty is to determine its bounds.' Here

in deciding a question before which science stands helpless. Ignorance cannot understand where the difficulty lies. 'Do I not know a cow from a cabbage, a tree from a tortoise? Is not an animal an animal, a plant a plant?' Nor did even science, some years ago, feel any difficulty. Vegetables,' said the great Linnæus, are organized and live; animals are organized, live, feel, and move.' These characters were decisive enough, or seemed so, until it was shown that some plants move and some animals are fixed. On this hear the Professor :

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:

Not only are most polypes and a few echinoderms adherent to the place of their growth, but the whole class of cirripedes and some genera both of articulate and molluscous animals, e. g. Serpula and Ostrea, are cemented by their shells as immoveably to the rock on which they grow as are the seaweeds that float beside them from their adherent base. On the other hand, many microscopic single-celled plants, as well as the ciliated zoospores or enbryos of the Vaucheria and other algæ, and of the sponges, have a more rapid locomotion than some of the polygastric animalcules enjoy; although in neither case, probably, does it arise from a distinct act of volition. The movements of the oscillatoriæ, and the more partial shrinkings of the sensitive plant from the touch, show that 'motion' merely, whether of the whole or of the parts of a living organism, will not determine to which kingdom it belongs.

Nor will the character of 'feeling' settle the point; for if we extend the term feeling so as to embrace in it the contractility of the lowest animals, we cannot refuse it also to plants.

Baffled thus in their attempts to find a dynamic character which would serve as a test, philosophers directed their attention to the static characters, and sought in the elementary structures of plants and animals to find a distinction; but in vain. One by one the supposed distinctions have vanished. We need not enumerate them, but confine ourselves to the one most generally accepted-namely, that animals absorb oxygen and exhale carbonic acid; plants on the contrary absorb carbonic acid and exhale oxygen. This delightful parallelism of complementary processes has been much

1856.]

admired; the rhetoric expended on it has been immense. But alas! it is not true. It is only the rough approximation to truth which suffices for ordinary language, and which the rigorous precision of science disowns. We anticipate the reader's expressions of astonishment on hearing that the wellknown fact' of animals and plants being thus opposed as regards respiration is not true; let him be patient, and the explanation will calm him. Professor Owen, noticing the balance of gases maintained by the antagonistic action of animals and plants, says, 'In a general way this is true, but the chemical antagonism fails as a boundary line where we most require it, as we approach-viz., the confines of the two kingdoms.' And he adds,

Wöhler has shown that some of the free and locomotive polygastria, e. g., Chlamidomonas pulvisculus, Eugleno viridis, Frustulia salina, eliminate pure oxygen as the ultimate metamorphosis of their_tissues and, on the other hand, Drs. Schlossberger and Döpping have proved that mushrooms and sponges exhale carbonic acid.'

The Professor limits his argument to those creatures which lie at the confines of the two kingdoms. We venture further, and deny that there is antagonism in the respiratory process even between the highest animals and plants; and as in supporting this denial we shall put the reader in possession of curious and novel facts, he will more readily give us his attention. It is now not only ascertained that the green parts of plants absorb carbonic acid and give off oxygen (under the stimulus of solar light), but also that the parts not green, both day and night, reverse the process, giving off carbonic acid, and absorbing oxygen, just like the lungs of animals. This double process usually escapes observation, because the exhalation of oxygen, in daylight, is so much greater than the exhalation of carbonic acid, that it usurps consideration; and in rough approxi

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mative speech we say plants do not exhale carbonic acid,' just as we say the stars are hidden in daytime, although we know them to be shining as brightly as at night. It is enough, however, to know that plants do exhale carbonic acid and absorb oxygen-a knowledge which destroys the pretended line of de

marcation.

The

Nay, more: if we confine ourselves to the fundamental process of respiration - namely, the exchange of the two gases-we shall arrive at the curious conclusion that animals also manifest the twofold process observable in plants; animals also, in different parts of their organism, exhaling both oxygen and carbonic acid! This paradox admits of easy verification. capillary vessels in the lungs of animals absorb the oxygen from the atmosphere, and give out in exchange carbonic acid. This is supposed to be the whole fact of animal respiration, just as the exhalation of oxygen and absorption of carbonic acid was until lately supposed to be the whole fact of plant-respiration. But it is only one process; the capillaries which carry the absorbed oxygen to the tissues, instead of acting like the capillaries of the lungs, completely reverse the process, giving out their oxygen, and taking in exchange the carbonic acid which has been formed by the action of the tissues. Thus animals as well as plants manifest the twofold process of respiratory exchange and to bring the parallelism closer, we will add that it is the analogous parts of each which perform the same process: for the green parts of plants, which absorb carbonic acid, are the centres of nutritive changes, so are the capillaries of the tissues; whereas the other parts of plants are mere exhaling surfaces, like the lungs, and both exhale carbonic acid.

In propounding so novel a view of the relation between animals and plants, we must not overlook the difference which exists even in the parallelism-namely, that the plant

absorption of carbonic acid is from the atmosphere, whereas the animal absorption of carbonic acid is from within its own organism. The plant absorbs carbonic acid to fix the carbon in its tissues: the animal, to liberate from its tissues the carbon which has become carbonic acid in functional activity. Hence the preponderance in the plant of a process which in the animal is quite secondary, and the preponderance in the animal of a process which in the plant is insignificant; and thus approxima tively it is right to say animals exhale carbonic acid, plants oxygen. When however we reflect that in animals the waste of tissue consequent on activity is incessant, whereas the waste of tissue in plants is scarcely appreciable, we see a reason for the great differences in the amount of carbonic acid thrown off by the two. In animals the process of oxydation, although unquestionably supreme, is nevertheless accompanied by a process of deoxydation on a much smaller scale.* In plants it is just the reverse: the deoxydating process is in them preponderant, although accompanied by a feeble oxydation.

Not only the view, but the facts just stated will be novel to many readers, who having long been taught that carbonic acid is formed in the lungs, the carbon being burnt there by the oxygen of the atmosphere,or that it is formed elsewhere in the blood by the absorbed oxygen, will dispute the statement of the capillaries absorbing carbonic acid in exchange for oxygen. They are referred to Lehmann's great work on Organic Chemistry for proof. We cannot pause here to detail the reasons, but pass on to Professor Owen's next point. He has proved by what we have already cited, that respiration is no infallible test of animality or vegetality. Can food furnish us with such a test?

The physiologist has asserted that plants alone can subsist on inorganic matter, and that animals depend upon plants for combining the elements into binary and ternary compounds essential to animal support. And this also is in some degree true: the lichen that first

clothed the granite rock must have converted the inorganic elements into cellular tissue. Animals, as a general rule, subsist on vegetable or on animal matter, or on both. But no proof has been given that the Frustulia and other astomous polygastria, which separate oxygen in excess, do not effect this by reducing the carbonic acid of the atmosphere, and fixing the carbon, in order to produce their fats and hydrates of carbon; or that they do not, in like manner, assimilate their ammonia either directly, or by taking the nitrogen of the atmosphere into the required combination; and so by its subsequent combination with the elements of the fats and hydro-carbonates, produce their proteine compounds and albuminates. Still less proof or probability have we that the typical or higher organized forms of vegetation could flourish without the support of decaying organized tissues, superadded to the air and water.

Again we are disposed to go further, and declare that all such distinctions are illusory, for animals do feed on inorganic matter; not exclusively, not even largely, but universally and inevitably. What is the water we drink, the oxygen we breathe, the salts and earths we eat in our food and with our food, but inorganic matter? Every cell of the organism has its necessary proportion of inorganic matter. Chossat in his celebrated experiments, found that pigeons deprived of all chalk except what they got in their food, gradually died of starvation. Every farmer will tell you how indispensable salt is to cattle.

We may then exclaim with the Professor that after reviewing the different characters by which it has been attempted to distinguish the special subjects of the botanist and zoologist, we find that neither sensation and motion, the internal assimilating cavity, the respiratory products, the chemical constitution of the tissues, nor the source of nutriment, absolutely and unequivocally define the boundary between the animal and vegetable kingdoms. We can only recognise the plant or animal when a certain number of their supposed characteristics are combined together.' Animals and plants do not form two natural divi