Societies and Academies

    Abstract

    LONDON. Royal Society, January 15.—Sir Charles Sherrington and E. G. T. Liddell: Further observations on myo-tatic reflexes. The myotatic reflex of the knee-extensor obtains after pre-collicular as well as after inter-collicular transection. The reflex retains tonic character after exclusion of the otic labyrinths. Stretch of the knee-flexors also yields a myotatic reflex, a main action of which is the depression by inhibition of the myotatic reflex of their antagonist, the knee-extensor. The reflex relaxation of the knee-extensor thus obtained is not changed into contraction by administration of strychnine.-A. V. Hill, C. N. H. Long, and H. Lupton: Muscular exercise, lactic acid, and the supply and utilisation of oxygen. An attempt is made to apply to the case of muscular exercise in man the principles discovered in the last seventeen years by the physical and chemical investigation of activity in the isolated frog's muscle. Part I. summarises the investigations, especially such as refer to the recovery process by which lactic acid, liberated during exercise, is removed in the presence of oxygen afterwards. In Part II. is described the method of estimating lactic acid in human blood. Part III. is a description of the lactic acid changes which occur in human blood, during and after exercise, with an account of their effect on the respiratory quotient. Part IV. describes methods of studying the respiratory exchanges in man, under the rapidly altering conditions which obtain at the beginning and end of exercise. Part V. is an account of the recovery process, in which oxygen is used and the lactic acid produced during activity is restored as the glycogen from which it arose. In Part VI. a discussion is given of the "oxygen debt "existing at the end of exercise, and of the muscle as an "accumulator of energy."Part VII. describes the relation between the rate of oxygen intake and the intensity of exercise. Considerably increased amounts of oxygen can be taken in when breathing gas mixtures rich in oxygen. In Part VIII. curves are given relating the "oxygen requirement "to the severity of various types of exertion.-A. P. Chattock: The physics of incubation. Daily cooling appears to be unnecessary, but an improvement in the hatching of more than n per cent, is indicated if the usual twice-a-day turning is increased to four times at equal intervals. By means of specially designed hygrometers, values of the humidity under hens have been obtained; very little improvement resulted from raising the humidity in incubators to the hen's nest value (20 mm. water-vapour pressure at the centre). On the principle that the water vapour and carbon dioxide which escape from the eggs during incubation must both leave the nest by the same paths, the ventilation in a hen's nest may be estimated. The value obtained is equivalent to the passage through the nest of 3-2 cubic feet of air per hour per 50 eggs; and is several times smaller than the ventilating air flow in typical "hot air "and "tank "incubators.-J. F. Fulton: (i) The influence of tension upon the electrical responses of muscle to repetitive stimuli. Simultaneous mechanical and electrical records of short, maximal, tetanic responses of intact skeletal muscle (gastro-cnemius and sartorius; frog) have shown that the sue of the successive electrical responses varies in isometric contraction with the tension developed, and in isotomic records with the work done. Tension per se rather than length of fibre controls the size of the action current. The mechanism which determines the size of the action current probably also controls the energy liberation within the fibre. (2) The relation between the durations of the isometric twitch and of the after-action of tetanus. The end of the plateau of short tetanic responses is characterised by an "angle "similar to that of the twitch. The duration of the after-action as measured from the beginning of the last electrical response of the tetanus to the "angle "is, in short tetani, invariably less than the duration of the twitch. The ratio of these two durations is approximately the same as that of the size of the corresponding action currents. The terminal "angle "of long tetani is less precise than in short, and is also less precise at high initial tensions than at low tensions. These modifications of the "angle "may be taken as evidence of slight fatigue-a less prompt "neutralisation "of the activating ions. (3) Some observations upon the electrical responses and shape of the isometric twitch of skeletal muscle. Isometric twitches of the intact gastrocnemius of frogs, when recorded with a myograph of high natural frequency, have a flat top which terminates with sufficient abruptness to form on the linear record a clearly defined "angle."Any factor tending to produce fatigue, obscures the "angle."From the shape of the isometric twitch it has been inferred that the "fundamental "process of contraction is rectangular in shape, the "angle "representing the point at which it ends, and the curve of relaxation representing the viscous return of the muscle to its resting shape.

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    Societies and Academies. Nature 115, 141–143 (1925). https://doi.org/10.1038/115141a0

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