Alluding to one of Graham's recent discoveries, he said:-" The importance of this discovery in metallurgy, and its application to the physiology of respiration and of the passage of oxygen from the blood into the textures, must be apparent to all." But nothing could be more unlikely, on chemical grounds, than such a mode of oxidation. Oxygen, when just liberated from combination, is usually more active in entering into new combinations, and yet, here we are called upon to believe that a great portion of it leaves one combination without any assignable cause, and remains for a time in a free state, although present in the same solution with matters for which it has a great affinity. That the oxygen of the colouring matter is capable of combining directly with some of the nitrogenous compounds of the blood, is evident from an experiment of Stokes's, in which a solution of blood was found to reduce itself when preserved in a closed vessel. The experiment further proves that the oxidizing power of the blood is not necessarily dependent upon nerve-action, although it may, very probably, be stimulated by it. Mayer saw this difficulty in the current theory of tissue-oxidation, and met it by placing the seat of all oxidation in the blood, and by assigning to the corpuscles the office of effecting directly the whole of it. Both heat and muscular work derive their source, according to him, from blood-oxidation, some portion of the oxidation yielding work, the remainder heat. He says, "The muscle produces mechanical work at the expense of the chemical action expended in its capillary vessels." Claude Bernard seems to have adopted a similar view, and expresses it occasionally with great clearness. The following passage occurs in his celebrated Leçons sur les Liquides de l'Organisme:'t "Il est infiniment probable que l'acide carbonique du sang veineux résulte d'une oxydation qui s'est effectuée dans le globule sanguine lui-même. Lorsque le sang traverse les capillaires, il y aurait entre lui et les tissus non échange de gaz, mais peut-être échange de liquides. Par suite des conditions nouvelles que créerait cet échange, l'oxygène du globule serait en partie employé à oxyder le carbone du globule lui-même." This therefore is the third, and it appears to me the only tenable hypothesis of the source of muscular power. I shall speak of it as Mayer's hypothesis. The blood is the seat of all oxidation, and therefore the originator of all force in the body. Some part of this force is evolved in the form of muscular work, the greater part of * It is, however, right to add, that oxygen is probably held in cruorine, in what Kekulé calls "molecular combination," since it has been shown that carbonic oxide displaces from it its own volume of oxygen. In this case the liberated oxygen would not be more than usually active. Vol. i., 342. the remainder in that of heat. How it comes about that oxidation inside a capillary is converted into muscular movement outside, we do not know with certainty. The conversion is effected under the control of the nervous system, and we may therefore venture to suppose that some of the force set free during blood-oxidation may, through the agency of the nerves, take the form of electric currents, which are the direct agents in the muscular work. This, however, is little better than a guess, and as such is entitled to very little reliance. The function of the nerves is the most obscure of all physiological problems, and the difficulty which it presents in this particular hypothesis is not greater than that which enshrouds all others on the subject. The establishment of Mayer's hypothesis would of course render meaningless the controversy between the followers of Liebig and those of Traube, for as both fats and carbohydrates on the one side, and the products of muscle metamorphosis on the other, are oxidized in the blood, both may equally be supposed to be originators of muscular power. It becomes therefore a matter of the utmost importance to test Mayer's view by every means we possess. I think it is possible, by an extension of one of his own lines of argument, to approach very near to a demonstration of its truth. He pointed out that the fluid which passed out from the blood through the walls of the capillaries was afterwards returned to the blood through the lymphatics, and that the quantity of this exudate could therefore be measured by the quantity of lymph. In this way he calculated that not one per cent. of the blood left the blood vessels in the course of the circulation, and he therefore inferred that not less than 99-100ths of the total oxidation of the body must be affected inside the blood vessels. But this argument is not entirely satisfactory, for it might be objected that the exudate, small though it was in amount, carried with it a sufficient quantity of oxygen for the oxidation, and therefore for the work of the muscles. I have therefore suggested another, which appears to me much more convincing. I purposely exaggerate every element of the calculation, in order as far as possible to overstate the case against me. The first thing to be done is to estimate the extreme quantity of fluid which can be supposed to exude through the walls of the bloodvessels in twenty-four hours. We have better data for this purpose than Mayer possessed. Bidder and Schmidt estimate the quantity of lymph and chyle together daily added to the blood at 28 lbs. Of this 6 lbs. is chyle, which comes from the food, and may be left out of the calculation. But I will assume the quantity of lymph alone to be 30 lbs. It may be objected that some of the exudate may return directly to the capillaries without traversing the lymphatic system. If this be the case, the quantity so returned could not be large, as the blood flows at a considerable pressure a pressure which would tend to prevent such a return. Nevertheless, I will, on this supposition, double the amount already given, and take it at 60 lbs. A large proportion of this would arise from glands and other parts which do little or no muscular work; but this I neglect. Finally, it may be urged that some portion of the exudate may escape as perspiration without returning to the blood at all. I therefore add 6 lbs. to obviate this source of error, and thus get a total daily exudate of 66 lbs. or 30 kilogrammes, an amount which I think every physiologist will admit is an extreme overstatement. How much oxygen can possibly be supposed to pass out in solution in this 30 kilogrammes of exudate? Berzelius found that the serum of blood would not dissolve more oxygen than water would. This would give as the quantity of oxygen exuded in 24 hours, less than I grammes; but I will assume that the exudate will dissolve 20 times as much oxygen as this, in fact, that it will absorb more than the moist corpuscles of the blood of the portal vein, which are superior to all others in this respect. The estimate is so extravagant that it is almost absurd to make it. It gives, as the daily exudate of oxygen through the muscles, 25.74 grammes. If the work of the muscles is done by oxidation outside the walls of the capillaries, it must all be done by this quantity of oxygen, and it is easy to show that the quantity is entirely insufficient for the purpose, whether it were employed in the oxidation of muscle or of fat. 25.74 grammes of oxygen would oxidize 17.31 grammes of muscle, and thus yield a force of 31,210 metre-kilogrammes, or 8.87 grammes of fat, and thus yield a force 34,070 metre-kilogrammes. To compare with this I will give an extremely low estimate of the work accomplished in the body in 24 hours, omitting doubtful items: Work of the heart (Donders) Work of the muscles Metre-kilogrammes. 70,000 10,000 20,000 100,000 The force actually generated to effect this work must, as Haidenhain has shown, be at least double the above quantity, so that even upon this extravagant calculation, the oxygen, which may be supposed to pass out from the capillaries to the muscular tissues, can only account for about one-sixth of the work done by the muscles. The establishment of Mayer's hypothesis would unfortunately not help us much in the solution of the practical question, What kind of food is most suitable for the man who does hard work? Both flesh-formers and heat-givers are available for the purpose, and provided the former are sufficient to repair the daily waste of the tissues, it is possibly immaterial which is employed. Even this, however, is not certain, and as we are still ignorant of the exact relation which tissue disintegration bears to work, we cannot as yet pretend to determine à priori the quantity of flesh-formers necessary under conditions of work. The practical solution which experience has provided for the problem must for the present rule our dietary scales, although it can hardly be doubted that a more scientific knowledge upon the subject will before long be gained. IV. LIGHT AND DARKNESS. WINSLOW ON LIGHT.*-JOHNS ON THE BLIND.t REGARDING the nature of Light, there have been, and perhaps may still be said to be, two distinct theories extant. The older view conceives of light as a form of matter, infinitely diffused, but still matter, which is itself projected from the light-emitting body, and falls upon the surrounding objects; the newer theory treats light as a force, and necessitates the belief in an interplanetary Ether, also a form of matter infinitely attenuated, but capable of being agitated in waves by the luminous force. The latter or undulatory theory of light, which makes it to be a mode of motion, is now almost completely established, and although the human mind cannot yet form a proper conception of the interplanetary ether, the medium acted upon, still that may be said also to be one of the acknowledged facts of physical science. Around this subject cluster many eminent reputations; that of Newton stands out the most prominent; it was he who first analyzed a ray, and showed it to be far more complicated than it appeared to be without the intervention of the prism. The elder Herschel and Ritter revealed the character of the non-luminous but calorific, and chemical, or as Robert Hunt has called them, the Actinic Rays. Stokes, Hunt, Locke, Joule, Balfour Stewart, Tyndall, and many others, have added to our knowledge of the nature and effect of light; and yet that knowledge is but in its infancy. Wonderful as are the operations of light upon inanimate nature, operations which have caused it to be employed in photography to perpetuate the memory of the living and to recall most vividly the history of the past; still more wonderful is its influence upon living forms, whether in the animal or plant world. * Light-its Influence on Life and Health.' By Forbes Winslow, M.D., D.C.L., Oxon. Longmans. + Blind People: their Works and Ways, with Sketches of the Lives of Some Famous Blind Men.' By Rev. B. G. Johns, M.A., Chaplain of the Blind School, St. George's Fields. Illustrated. John Murray. Its absence or presence causes marked modifications, not only in the colours of plants, but in their growth. It attracts vegetable forms or parts of them in the most extraordinary manner, and with recurring regularity. A wonderful sight, well known to microscopists, is that of the little volvox-globator, gathered in a green mass towards the light when some water containing these exquisite forms is exposed to its influence. Every child has watched the sunflower as its great round face is turned, as though by some machinery within, and follows the orb of day in its course through the heavens; and does not the gastronomic epicure well know that his asparagus, if carefully bedded up and kept in darkness, will not have the green hue which it assumes as soon as its head peeps above the soil? And as to men and animals, we have only to look at the stunted creatures of the dark and cold regions of the world; or at those who are bred underground or in the dismal courts of large cities in our own temperate zone, to be satisfied that with light we have robust, strong, and well-developed bodies; and without it, the reverse of these qualities. As we have already stated, the undulatory theory of light is now the accepted theory; and although the nature of the interplanetary ether which fills all space is a matter of individual conception, yet the presence of some such medium must be recognized along with the dynamic theory. And when we come to consider the nature of those material forms and organizations which must be permeated by that infinitely attenuated form of matter before light can penetrate them, and compare some of the transparent solids with fluids or gases which are only partially translucent, we become still more puzzled to understand the character of the medium upon which the force acts that we term light. The arrangement of the atoms which exclude it from one portion of our precious organ of sight, and concentrate it in another, are truly marvellous, and sad indeed is the fate of the creature in whom the natural order of the parts is so disturbed, that whilst all is bright, heavenly, smiling light without, there is nought but gloom and darkness within. Dr. Winslow tells us but little worth remembering, and almost nothing that is new, concerning the physiological effect of Light, and sums up his information upon that portion of the subject with which we should have supposed him to be the best acquainted (namely, the influence of light upon the insane), with the admission that he knows little or nothing about it, and in these words, "I freely admit that placing but little faith in what has been recorded or said on the subject, I have not kept any systematic register as to the effect of different phases of the moon on the insane."* Of the modern theories of light we take him to be ignorant, for VOL. IV. * P. 233. 2 A |