Part 16 (1/2)
Do we gain anything by attempting to get rid of the idea of a special vital force because we find certain mutually convertible relations between forces in the body and out of it? I think not, any more than we should gain by getting rid of the idea and expression Magnetism because of its correlation with electricity. We may concede the unity of all forms of force, but we cannot overlook the fixed differences of its manifestations according to the conditions under which it acts. It is a mistake, however, to think the mystery is greater in an organized body than in any other. We see a stone fall or a crystal form, and there is nothing stranger left to wonder at, for we have seen the Infinite in action.
Just so far as we can recognize the ordinary modes of operation of the common forces of nature,--gravity, cohesion, elasticity, transudation, chemical action, and the rest,--we see the so-called vital acts in the light of a larger range of known facts and familiar a.n.a.logies.
Matteuecci's well-remembered lectures contain many and striking examples of the working of physical forces in physiological processes. Wherever rigid experiment carries us, we are safe in following this lead; but the moment we begin to theorize beyond our strict observation, we are in danger of falling into those mechanical follies which true science has long outgrown.
Recognizing the fact, then, that we have learned nothing but the machinery of life, and are no nearer to its essence, what is it that we have gained by this great discovery of the cell formation and function?
It would have been reward enough to learn the method Nature pursues for its own sake. If the sovereign Artificer lets us into his own laboratories and workshops, we need not ask more than the privilege of looking on at his work. We do not know where we now stand in the hierarchy of created intelligences. We were made a little lower than the angels. I speak it not irreverently; as the lower animals surpa.s.s man in some of their attributes, so it may be that not every angel's eye can see as broadly and as deeply into the material works of G.o.d as man himself, looking at the firmament through an equatorial of fifteen inches' aperture, and searching into the tissues with a twelfth of an inch objective.
But there are other positive gains of a more practical character. Thus we are no longer permitted to place the seat of the living actions in the extreme vessels, which are only the carriers from which each part takes what it wants by the divine right of the omnipotent nucleated cell. The organism has become, in the words already borrowed from Virchow, ”a sum of vital unities.” The strictum and laxum, the increased and diminished action of the vessels, out of which medical theories and methods of treatment have grown up, have yielded to the doctrine of local cell-communities, belonging to this or that vascular district, from which they help themselves, as contractors are wont to do from the national treasury.
I cannot promise to do more than to select a few of the points of contact between our ignorance and our knowledge which present particular interest in the existing state of our physiological acquisitions.
Some of them involve the microscopic discoveries of which I have been speaking, some belong to the domain of chemistry, and some have relations with other departments of physical science.
If we should begin with the digestive function, we should find that the long-agitated question of the nature of the acid of the gastric juice is becoming settled in favor of the lactic. But the whole solvent agency of the digestive fluid enters into the category of that exceptional mode of action already familiar to us in chemistry as catalysis. It is therefore doubly difficult of explanation; first, as being, like all reactions, a fact not to be accounted for except by the imaginative appeal to ”affinity,” and secondly, as being one of those peculiar reactions provoked by an element which stands outside and looks on without compromising itself.
The doctrine of Mulder, so widely diffused in popular and scientific belief, of the existence of a common base of all alb.u.minous substances, the so-called protein, has not stood the test of rigorous a.n.a.lysis. The division of food into azotized and non-azotized is no doubt important, but the attempt to show that the first only is plastic or nutritive, while the second is simply calorifacient, or heat-producing, fails entirely in the face of the facts revealed by the study of man in different climates, and of numerous experiments in the feeding of animals. I must return to this subject in connection with the respiratory function.
The sugar-making faculty of the liver is another ”catalytic” mystery, as great as the rest of them, and no greater. Liver-tissue brings sugar out of the blood, or out of its own substance;--why?
Quia est in eo Virtus saccharitiva.
Just what becomes of the sugar beyond the fact of its disappearance before it can get into the general circulation and sweeten our tempers, it is hard to say.
The pancreatic fluid makes an emulsion of the fat contained in our food, but just how the fatty particles get into the villi we must leave Brucke and Kolliker to settle if they can.
No one has shown satisfactorily the process by which the blood-corpuscles are formed out of the lymph-corpuscles, nor what becomes of them. These two questions are like those famous household puzzles,--Where do the flies come from? and, Where do the pins go to?
There is a series of organs in the body which has long puzzled physiologists,--organs of glandular aspect, but having no ducts,--the spleen, the thyroid and thymus bodies, and the suprarenal capsules. We call them vascular glands, and we believe that they elaborate colored and uncolored blood-cells; but just what changes they effect, and just how they effect them, it has proved a very difficult matter to determine. So of the noted glandules which form Peyer's patches, their precise office, though seemingly like those of the lymphatic glands, cannot be positively a.s.signed, so far as I know, at the present time.
It is of obvious interest to learn it with reference to the pathology of typhoid fever. It will be remarked that the coincidence of their changes in this disease with enlargement of the spleen suggests the idea of a similarity of function in these two organs.
The theories of the production of animal heat, from the times of Black, Lavoisier, and Crawford to those of Liebig, are familiar to all who have paid any attention to physiological studies. The simplicity of Liebig's views, and the popular form in which they have been presented, have given them wide currency, and incorporated them in the common belief and language of our text-books. Direct oxidation or combustion of the carbon and hydrogen contained in the food, or in the tissues themselves; the division of alimentary substances into respiratory, or non-azotized, and azotized,--these doctrines are familiar even to the cla.s.ses in our high-schools. But this simple statement is boldly questioned. Nothing proves that oxygen combines (in the system) with hydrogen and carbon in particular, rather than with sulphur and azote. Such is the well-grounded statement of Robin and Verdeil. ”It is very probable that animal heat is entirely produced by the chemical actions which take place in the organism, but the phenomenon is too complex to admit of our calculating it according to the quality of oxygen consumed.” These last are the words of Regnault, as cited by Mr. Lewes, whose intelligent discussion of this and many of the most interesting physiological problems I strongly recommend to your attention.
This single ill.u.s.tration covers a wider ground than the special function to which it belongs. We are learning that the chemistry of the body must be studied, not simply by its ingesta and egesta, but that there is a long intermediate series of changes which must be investigated in their own light, under their own special conditions. The expression ”sum of vital unities” applies to the chemical actions, as well as to other actions localized in special parts; and when the distinguished chemists whom I have just cited ent.i.tle their work a treatise on the immediate principles of the body, they only indicate the nature of that profound and subtile a.n.a.lysis which must take the place of all hasty generalizations founded on a comparison of the food with residual products.
I will only call your attention to the fact, that the exceptional phenomenon of the laboratory is the prevailing law of the organism.
Nutrition itself is but one great catalytic process. As the blood travels its rounds, each part selects its appropriate element and transforms it to its own likeness. Whether the appropriating agent be cell or nucleus, or a structureless solid like the intercellular substance of cartilage, the fact of its presence determines the separation of its proper const.i.tuents from the circulating fluid, so that even when we are wounded bone is replaced by bone, skin by skin, and nerve by nerve.
It is hardly without a smile that we resuscitate the old question of the 'vis insita' of the muscular fibre, so famous in the discussions of Haller and his contemporaries. Speaking generally, I think we may say that Haller's doctrine is the one now commonly received; namely, that the muscles contract in virtue of their own inherent endowments. It is true that Kolliker says no perfectly decisive fact has been brought forward to prove that the striated muscles contract without having been acted on by nerves. Yet Mr. Bowman's observations on the contraction of isolated fibres appear decisive enough (unless we consider them invalidated by Dr. Lionel Beale's recent researches), tending to show that each elementary fibre is supplied with nerves; and as to the smooth muscular fibres, we have Virchow's statement respecting the contractility of those of the umbilical cord, where there is not a trace of any nerves.
In the investigation of the nervous system, anatomy and physiology have gone hand in hand. It is very singular that so important, and seemingly simple, a fact as the connection of the nerve-tubes, at their origin or in their course, with the nerve-cells, should have so long remained open to doubt, as you may see that it did by referring to the very complete work of Sharpey and Quain (edition of 1849), the histological portion of which is cordially approved by Kolliker himself.
Several most interesting points of the minute anatomy of the nervous centres have been laboriously and skilfully worked out by a recent graduate of this Medical School, in a monograph worthy to stand in line with those of Lockhart Clarke, Stilling, and Schroder van der Kolk. I have had the privilege of examining and of showing some of you a number of Dr. Dean's skilful preparations. I have no s.p.a.ce to give even an abstract of his conclusions. I can only refer to his proof of the fact, that a single cell may send its processes into several different bundles of nerve-roots, and to his demonstration of the curved ascending and descending fibres from the posterior nerveroots, to reach what he has called the longitudinal columns of the cornea. I must also mention Dr.
Dean's exquisite microscopic photographs from sections of the medulla oblongata, which appear to me to promise a new development, if not a new epoch, in anatomical art.
It having been settled that the nerve-tubes can very commonly be traced directly to the nerve-cells, the object of all the observers in this department of anatomy is to follow these tubes to their origin. We have an infinite snarl of telegraph wires, and we may be reasonably sure, that, if we can follow them up, we shall find each of them ends in a battery somewhere. One of the most interesting problems is to find the ganglionic origin of the great nerves of the medulla oblongata, and this is the end to which, by the aid of the most delicate sections, colored so as to bring out their details, mounted so as to be imperishable, magnified by the best instruments, and now self-recorded in the light of the truth-telling sunbeam, our fellow-student is making a steady progress in a labor which I think bids fair to rank with the most valuable contributions to histology that we have had from this side of the Atlantic.
It is interesting to see how old questions are incidentally settled in the course of these new investigations. Thus, Mr. Clarke's dissections, confirmed by preparations of Mr. Dean's which I have myself examined, placed the fact of the decussation of the pyramids--denied by Haller, by Morgagni, and even by Stilling--beyond doubt. So the spinal ca.n.a.l, the existence of which, at least in the adult, has been so often disputed, appears as a coa.r.s.e and unequivocal anatomical fact in many of the preparations referred to.
While these studies of the structure of the cord have been going on, the ingenious and indefatigable Brown-Sequard has been investigating the functions of its different parts with equal diligence. The microscopic anatomists had shown that the ganglionic corpuscles of the gray matter of the cord are connected with each other by their processes, as well as with the nerve-roots. M. Brown-Sequard has proved by numerous experiments that the gray substance transmits sensitive impressions and muscular stimulation. The oblique ascending and descending fibres from the posterior nerve-roots, joining the ”longitudinal columns of the cornua,” account for the results of Brown-Sequard's sections of the posterior columns. The physiological experimenter has also made it evident that the decussation of the conductors of sensitive impressions has its seat in the spinal core, and not in the encephalon, as had been supposed. Not less remarkable than these results are the facts, which I with others of my audience have had the opportunity of observing, as shown by M. Brown-Sequard, of the artificial production of epilepsy in animals by injuring the spinal cord, and the induction of the paroxysm by pinching a certain portion of the skin. I would also call the student's attention to his account of the relations of the nervous centres to nutrition and secretion, the last of which relations has been made the subject of an extended essay by our fellow countryman, Dr. H.