UNIVERSITY OF BIRMINGHAM.

LECTURER AND DEMONSTRATOR IN BREWING AND THE BIOCHEMISTRY OF FERMENTATION. GRADE III.

THE

HE COUNCIL invites Applications for the above post. Commencing stipend £300 per annum.

Applications, with testimonials, should be sent to the undersigned not later than the 25th September, 1922. No special form of application is required. Not more than three copies of testimonials need be sent and these need not be printed.

The candidate elected will be required to enter upon his duties on the 2nd October, 1922. The duties will include the analysis of brewing waters, materials, etc., which are sent from time to time to the Department.

The conditions of appointment for Grade III. and for promotion to Grade II. on the University Staff may be obtained. GEO. H. MORLEY, Secretary.

from

The University, Birmingham,

September, 1922.

BACK

WE FOR SALE a lL

THE CHEMICAL NEWS,

VOL. CXXV., No. 3256

BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE: HULL, 1922.

THE PRESIDENTIAL ADDRESS. SOME ASPECTS OF ANIMAL MECHANISM.

By Professor Sir C. S. Sherrington, G.B.E., Sc.D., D.Sc., LL.D., Pres.R.S., President of the Association.

are

It is sometimes said that Science lives too much to itself. Once a year it tries to remove that reproach. The British Association meeting is that annual occasion, with its opportunity of talking in wider gatherings about scientific questions and findings. Often the answers are tentative. Commonly questions most difficult those that can be quite briefly put. Thus, "Is the living organism a machine?" life the running of a mechanism?" answer cannot certainly be as short as the question. But let us, in the hour before us, examine some of the points it raises. Of course for us the problem is not the why of the living organism but the how of its working. If we put before ourselves

'Is

The

some aspects of this working we may judge for ourselves some at least of the contents of the question. It might be thought that the problem is presented at its simplest in the simplest forms of life. Yet it is in certain aspects more seizable in complex animals than it is in simpler forms. let us turn thither.

And so

Our own body is body is full of exquisite mechanism. Many exemplifications could be chosen. There is the mechanism by which the general complex internal medium, the blood, is kept relatively constant in its chemical reaction, despite the variety of the food replenishing it and the fluctuating draft from and input into it from various organs and tissues. In this mechanism the kidney cells and the lung cells form two of the main sub-mechanisms.

And one part

of the latter is the delicate mechanism linking the condition of the air at the bottom of the lungs with that particular part of the nervous system which manages the ventilation of the lungs. On that ventilation depends the proper respiratory condition of

ness.

the blood. The nervous centre which manages the rhythmic breathing of the chest is so responsive to the respiratory state of the blood supplied to itself that, as shown by Drs. Haldane and Priestley some years ago, the very slightest increase in the partial pressure of carbon dioxide at the bottom of the lungs at once suitably increases the ventilation of the chest. And dovetailed in with this mechanism is a further one working for adjustment in the same direction. As the lung is stretched by each inbreath the respiratory condition of the nervous centre, already attuned to the respiratory quality of the air in the lungs, sets the degree to which inspiration shall fill them ere there ensue the opposite movement of outbreath. All this regulation, although the nervous system takes part in it, is a mechanism outside our consciousPart of it is operated chemically; part of it is reflex reaction to a stimulus of mechanical kind, though as such unperceived. The example taken has been nervous mechanism. If in the short time at disposal we confine our examples to the nervous system, to do so will have the advantage that in one respect that system presents our problem possibly at its fullest. To turn therefore to another instance, mainly nervous. Muscles execute our movements; maintain they also postures. This postural action of muscles is produced by nerve-centres which form a system more or less their own. One posture of great importance thus maintained is that of standing, the erect possure. This involves due co-operation of many separate muscles in many parts. Even in absence of those portions of the brain to which consciousness is adjunct the lower nervecentres successfully bring about and maintain all this co-operation of muscles whichresults in the erect posture. For instance, the animal in this condition, if set on its feet, stands. It stands reflexly. More than that, it adjusts its standing posture to required conditions. If the pose of one of the limbs be shifted, that shift induces a compensatory shift in the other limbs, so A turn of the that stability is retained.

our

creature's neck sidewise and the body and limbs of themselves take up a fresh attitude appropriate to the side-turned head. Each particular pose of the neck telegraphs off to the limbs and body a particular posture required from them, and that posture is then maintained so long as the neck posture is maintained. Stoop the creature's

neck and the forelimbs bend down as if to seek something on the floor. Tilt the muzzle upward and the forelimbs straighten and the hind limbs crouch as if to look up at a shelf. Purely reflex mechanism provides most kinds of ordinary postures.

The

Mere reflex action provides these harmonies of posture. The nerve-centres evoke for this purpose in the required muscles a mild, steady contraction, with tension largely independent of the muscle length and little susceptible to fatigue. Nerve-fibres run from muscle to nervecentre. By these each change in tension or length of the muscle is reported to the activating nerve-centre. They say,Tension rising, you must slacken, or conversely. There also play a part organs whose stimulation changes with change of their relation to the line of gravity. Thus, a pair of tiny water-filled bags set one in each side of the skull. In each of these a patch of cells endowed with a special nerve. Attached to hairlets of these cells a tiny crystalline stone whose pressure acts as a stimulus through them to the nerve. nerve of each gravity-bag connects, through chains of nerve-centres, with the muscles of all the limbs and of one side of the neck. In the ordinary erect posture of the head the stimulation by the two bags right and left is equal, because the two gravitystones then lie symmetrically. The result, then, is a symmetrical muscular effect on the two sides of the body, namely, the normal erect posture. But the right and left bags are mirror pictures of each other. If the head incline to one side the resulting slip, microscopic though it be, of the two stones on their nerve-patches makes the stimulation unequal. And from that slip there results exactly the right unsymmetrical action of the muscles to give the unsymmetrical pose of limbs and trunk ind neck. An additional one postures the head itself on the neck; a second pair of tiny gravity-bags, in which the stones hang rather than press. These, when any cause inclining the head has passed, bring the head back at once to the normal symmetry of the erect posture. And these same bags manage the posturing of the eyes. The eye contributes to our orientation in space; for instance, to perception of the vertical. And for this the eyeball, that is the retina, bas to be postured normally. The pair of little gravity-bags in the skull, which act to restore the head posture, act also on the eyeball muscles. Whichever way the head

turns, slopes, or is tilted, these adjust the eyeball's posture compensatingly, so that the retina still looks out upon its world from an approximately normal posture, retaining its old verticals and horizontals. As the head twists to the right the eyeball's visual axis untwists from the right. These reactions of head of head and eyes and body unconsciously take place when a bird wheels or slants in flight or a pilot stalls or banks his aeroplane. And all this work itself involuntarily as a pure mechanism, whose analysis we owe mainly to Prof. Magnus and Dr. de Kleijn, of Utrecht.

True, in such a glimpse of mechanism what we see mainly is how the machinery starts and what finally comes out of it; the intermediate elements of the process we know less of. Each insight into mechanism reveals more mechanism still to know.

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Thus, hardly was the animal's energy balance in its bearing upon food intake shown comfortably to conform with thermodynamics than came evidence of the socalled vitamines." Unsuspected influence on nutrition by elements of diet taken in quantities so small as to make their mere calorie value quite negligible; thus, for the growing rat, to quote Professor Harden, a quantity of vitamin A of the order of milligram a day. Again, as regards sex determination, the valued discovery of a visible distinction between the nuclear threads of male and female brings the further complexity that in such cases sex extends throughout the whole body to every dividing cell. Again, the association of hereditary unit-factors, such as body colour or shape of wing, to visible details in the segmenting nucleus seemed to simplify by epitomising. But further insight tends to trace the inherited unit character not to the chromosome itself, but to balance of action between the chromosome group. As with the atom in this heroic age of physicists, the elementary unit assumed simple proves, under further analysis, to be itself complex. Analysis opens a vista of further analysis required. Knowledge of muscle contraction has, from the work of Fletcher and Hopkins on to Hill, Hartree, Meyerhof, and others, advanced recently more than in many decades heretofore. The engineer would find it difficult to make a motive machine out of white of egg, some dissolved salts, and thin membrane. Yet this practically is what Nature has done in muscle, and obtained a machine of high mechanical efficiency. Perhaps human ingenuity can

learn from it. One feature in the device is alternate development and removal of acidity. The cycle of contraction and relaxation lies traced to the production of lactic acid from glycogen and its neutralisation chiefly by alkaline proteins; and physically to an admirably direct transition from chemical to mechanical effect. What new steps of mechanism all this now opens! To arrive at one goal is to start for others.

But knowledge, while making for complexity, makes also for simplification. There seems promise of simplification as to the mechanism of reflex action. Reflex action with surprising nicety calls into play just the appropriate muscles, and adjusts them in time and in the suitable grading of their strength of pull. The moderating as well as the driving of muscles is involved. Also the muscles have to pass from the behest of one stimulus to that of another, even though the former stimulus still persist. For these gradings, coadjustments, restraints, and shifts various separate kinds of mechanism were assumed to exist in the nerve-centres, although of the nature of such mechanisms little could be said. Their processes were regarded as peculiar to the nerve-centres and different from anything that the simple fibres of nerve-trunks outside the centres can produce. We owe to Lucas and Adrian the demonstration that without any nerve-centre whatever an excised nerve-trunk with its muscle attached can be brought to yield, besides conduction of nerve impulses, the extinction or attenuation or augmentation of them. That is remarkable, because the impulse is not gradable by grading the strength of the stimulus. Any stimulus of strength sufficient to excite the nerve-fibre at all, excites in it an impulse which is the fullest which the nerve-fibre can at the time give. energy of the impulse comes not from the stimulus, but from the fibre itself. Lucas and Adrian have shown it gradable in another way. Though the nerve impulse is a quite brief affair-it lasts about

The

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second at any one point of the nerve-it · leaves behind it in the nerve-fibre a short phase during which the fibre cannot develop a second impulse. Then follows rapid but gradual recovery of the strength of impulse obtainable from the fibre. That recovery may swing past normal to super-normal before final return to the old resting state. Hence, by appropriately timing the arrival of a second impulse after a first, that second impulse may be extinguished or re

duced or increased or transmitted without alteration. This property of grading impulses promises a complete key to reflex action if taken along with one another. The nervous system, iicluding its centres, consists of nothing but chains of cells and fibres. In these chains the junctions of the links appear to be points across which a large impulse can pass, though a weak one will fail. At these points the grading of impulses by the interference process just outlined can lead, therefore, to narrowing. or widening of their further distribution, much as in a railway system the traffic can be blocked or forwarded, condensed or scattered. Thus the distribution and quantity of the muscular effect can be regulated and shifted not only from one muscle to another, but in one and the same muscle can be graded by adding to or subtracting from the number of fibres activated within that muscle. As pointed out by Prof. Alexander Forbes, it may be, therefore, that the nerve impulse is the one and only reaction throughout the whole nervous system, central and peripheral, trains of impulses simply interfering, colliding and over-running as they travel along the inter-connected branches of the conductive network. In this may lie the secret of the co-ordination of reflexes. The nerve-centre seems nothing more than a meeting-place of nervefibres, its properties but those of impulses in combination. Fuller knowledge of the mechanism of the nervous impulse, many of whose physical properties are now known, a reaction open to study in the simplest units of the nervous system, thus leads to a view of nervous function throughout that system much simpler than formerly obtained.

They

Yet for some aspects of nervous mechanism the nerve impulse offers little or no clue. The fibres of nerve-trunks are perhaps of all nerve-structures those that are best known. They constitute, for instance, the motor nerves of muscle and the sensory nerves of the skin. When they are broken the muscle or skin is paralysed. establish their ties with muscle and skin during embryonic life. These ties they then maintain practically unaltered throughout the individual's existence, and show no further growth. If severed, say, by a wound, they die for their whole length between the point of severance and the muscle or skin they go to. And then at once the cut ends of the nerve-fibres start re-growing from the point of severance, al