Abstract
LONDON. Royal Society, November 5.—L. Ballif, J. F. Fulton, and E. G. T. Liddell: Observations on spinal and decerebrate knee-jerks, with special reference to their inhibition by single break-shocks. Simultaneous mechanical torsion-wire myograph and electrical records have been obtained of knee-jerks in decerebrate and spinal preparations. The spinal knee-jerk differs from the decerebrate: the mechanical response of the spinal jerk is two to three times longer in duration than that of the decerebrate jerk (or the motor twitch); the curve of relaxation of the spinal jerk is different; the electrical response tends to be more prolonged in the spinal knee-jerk; the interval between the tap and the electrical response is greater in the spinal preparations; and the spinal jerk is more difficult to elicit. The shortest spinal knee-jerk observed seems to be produced by a repetitive discharge of at least 4 to 8 volleys of impulses recurring somewhat asynchronously at 100 to 200 per sec. Both spinal and decerebrate knee-jerks may be inhibited by a single appropriately timed break-shock applied to an ipsilateral afferent nerve, the former much more readily than the latter. When recovering from an inhibition, the spinal knee-jerk has the same duration as a twitch or a decerebrate knee-jerk.— K. Furusawa: (i) Muscular exercise, lactic acid, and the supply and utilisation of oxygen. Pt. xiii. The gaseous exchanges of restricted muscular exercise in man. A simple ergometer, capable of being worked at any speed by the arms, has been constructed. As regards oxygen requirement, there is a marked optimal speed but no optimal load. Oxygen intake rises much more slowly to its maximum value than it does in the case of exercise involving most of the muscles of the body. It seems that lactic acid produced in excess by violent activity of a localised group of muscles may diffuse from them into the blood, and thence to other parts of the body (particularly resting muscles and liver), and there be removed or restored to glycogen under the influence of oxidation occurring in those tissues. There appears, therefore, to be possibility of an exhaustion due to complete using up of lactic-acid precursor, when the exercise involved is localised in a small group of muscles. (2) A spirometer method of studying continuously the gaseous metabolism of man during and after exercise. A new method is described of studying continuously the rapidly altering gaseous metabolism of man during and after muscular exercise. A spirometer of large capacity is used, the gases inside it being kept continuously stirred, the total ventilation being measured every 10 litres, and samples being abstracted at intervals for analysis.—D. T. Harris: The effect of light on the circulation. Irradiation of a localised area of skin with ultra-violet energy causes a widespread peripheral vaso-dilation. Consequently, only a very slight transitory rise of blood-pressure results from the small increase in pulse rate of from two to five per minute in dark and white subjects respectively. The reaction was always less in pigmented subjects. The vaso-dilator response to ultra-violet radiation is enhanced by a previous exposure; this is not the case with radiant heat. The vascular response appears to be a nervous reflex initiated by a nocuous stimulus; the whole phenomenon is one of incipient injury.—A. V. Hill: The surface tension theory of muscular contraction. The amount of lactic acid liberated when a muscle fibre i cm. long develops a force of i dyne is 1.46 ×10-11 gm. This is very nearly zo11 molecules. Spread out in a continuous mono-molecular film these would occupy about 2.1 x 10-4 sq. cm. If the mechanical response of muscle were due to a change of surface tension caused by such a film, the coefficient of surface tension required would be about 4800 dynes per centimetre. This is about 230 times the tension of a water— olive-oil interface, clearly an impossible value. Reckoned per gm. of muscle, the amount of lactic acid liberated in a maximal contraction of a frog's muscle is about 0.033 mgm. which would occupy an area of about 470 sq. cm.; i.e. about the surface area of the fibres composing the muscle.—J. F. Fulton and E. G. T. Liddell: Electrical responses of extensor muscles during postural (myotatic) contraction. Simultaneous mechanical and electrical records have been obtained of the responses of quadriceps femoris and rectus femoris of decerebrate cats to various forms of postural (myotatic) reflex. The knee-jerk seems to be produced by a somewhat asynchronous volley of impulses. The comparative absence of electrical responses in stretch reflex is due to complete asynchronism of afferent stimuli, for when a large number are recruited synchronously an action current invariably occurs. Since the exaggerated stretch reflex characteristic of the decerebrate condition is in large measure responsible for rigidity of extensor muscles in the decerebrate animal, we have inferred that these sustained postural reactions are produced by asynchronous all-or-nothing contractions of individual muscle fibres rather than by hypothetical fixing mechanisms.—L. N. Katz: On the supposed pluri-segmental innervation of muscle fibres. In the frog, when the two components of the sciatic nerve are stimulated in succession in an isometric tetanus, the sum of the tension developed is considerably greater than the tension produced when both components are stimulated simultaneously. The total heat developed on stimulating the two components of the sciatic nerve separately is, however, the same as that produced when they are stimulated simultaneously. This indicates that there is no pluri-segmental innervation of frog's muscle fibres apart from possible infrequent chance variations.—L. N. Katz and C. N. H. Long: Lactic acid in mammalian cardiac muscle. Pt. i. The stimulation maximum. The mammalian heart is dependent on its contemporary oxygen supply, and fails rapidly in its absence; the skeletal muscle, on the other hand, is independent at first of its contemporary oxygen supply. The data obtained from cats and rabbits show that the mean lactic-acid stimulation maximum of the heart is approximately one-third that of the skeletal muscle. The maximum “oxygen-debts” of these two tissues should therefore be in the same ratio.—H. J. G. Hines, L. N. Katz, and C. N. H. Long: Lactic acid in mammalian cardiac muscle. Pt. ii. The rigor mortis maximum and the normal glycogen content. The rigor mortis maximum, or the caffeine rigor maximum, of lactic acid in the heart is only half that in the skeletal muscle. A lack of lactic-acid precursor is not the cause of the relatively low stimulation maximum in the heart. The glycogen content of the heart is much smaller than that of skeletal muscle in well-fed cats. There is in the heart a greater discrepancy between resting glycogen content and the lactic acid produced in rigor mortis, than there is in skeletal muscle. It indicates that a greater portion of the lactic-acid precursor of the heart is in some other form than glycogen.—Phyllis Kerridge, L. N. Katz, and C. N. H. Long: Lactic acid in mammalian cardiac muscle. Pt. iii. Changes in hydrogen-ion concentration. The hydrogen-ion concentration of cardiac and of skeletal muscles stimulated to fatigue are different; the difference is of the order of o.2pH, the skeletal muscle being the more acid. In rigor mortis the difference is of the order of o.4pH, the skeletal muscle being the more acid. Cardiac and skeletal muscle have different buffering powers which vary at different pH's. The maximum difference is at approximately 6.3pH, when the ratio of the buffering power of skeletal to that of cardiac muscle is about 2: I.— W. E. Garner: The mechanism of muscular contraction. It is suggested that the tension generated on applying a stimulus to a muscle fibre is due to the formation of a solid film on the surfaces of the ultimate fibrils of the muscle. Liquid crystals composed of long-chain carbon compounds are present in the anisotropic segments of the muscle, and the molecules of the long-chain carbon compounds are orientated with their chains in a direction parallel to the axis of the fibre. It is suggested that glycogen is converted into sodium lactate according to the series of reversible reactions A ⇌ B ⇌ lactic acid, where A is a product formed from glycogen and B is an intermediate active form of both A and lactic acid. The direction of the chemical reaction may be influenced by alteration of the surface energy of the membranes during movements of the muscle. Wheri the energy liberated during the conversion of glycogen into lactic acid is not utilised in doing external work, it may be stored, in part, by a reversal of the reactions.—R. W. Riding and E. C. C. Baly: The occurrence of helium and neon in vacuum tubes. [Proc. A 749 (September), pp. 186-193.]—O. W. Richardson: Structure in the secondary hydrogen spectrum (iii.). [Proc. A 750 (October), pp. 239-266.] —T. R. Merton and J. G. Pilley: On the excitation of the band spectrum of helium. [Proc. A 750 (October), pp. 267-272.]—H. Hartley and J. E. Fraser: The conductivity of uni-univalent salts in methyl alcohol at 25° C. [Proc. A 750 (October), pp. 351-368.]—C. S. Beals: The arc spectrum of palladium. Its Zeeman effect and spectral type. [Proc. A 750 (October), pp. 369-384.]—N. Ahmad: Further experiments on the absorption and scattering of γ-rays. [Proc. A 749 (September), pp. 206-223.] —R. A. R. Tricker: A determination of the variation of the mass of the electron with velocity, using homogeneous β-rays. [Proc. A 750 (October), pp. 384-396.]—E. H. Boomer: Experiments on the chemical activity of helium. [Proc. A 749 (September), pp. 198-205.]—R. M. Wilmotte: On the construction of a standard high-frequency inductive resistance and its measurement by a thermal method. [Proc. A 751 (November), pp. 508-522.]—R. B. Erode: The absorption coefficient for slow electrons in the vapours of mercury, cadmium, and zinc. [Proc. A 750 (October), pp. 397-405.]—P. Kapitza and H. W. B. Skinner: The Zeeman effect in strong magnetic fields. [Proc. A 749 (September), pp. 224-239.]—F. R. Weston: The flame spectra of carbon monoxide and water gas. Pt. ii. [Proc. A 751 (November), pp. 523-526.]—H. S. Hirst and E. K. Rideal: The thermal decomposition of nitrogen pentoxide at low pressures. [Proc. A 751 (November), pp. 526-540.]—R. W. Gurney: The number of particles in the beta-ray spectra of radium B and radium C. [Proc. A 751 (November), pp. 540-561.]
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Societies and Academies. Nature 116, 733–735 (1925). https://doi.org/10.1038/116733a0
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DOI: https://doi.org/10.1038/116733a0