Herbert S. Gasser

The inseparability of the mechanical and thermal responses in muscle

OUR knowledge of the nature of the muscular mechanism is based on ,observations of such manifestations of its activity as tension, heat, electrical potential change, acidity and metabolism. It would be very useful in the analysis of the mechanism of contraction if states could be found in which the functions could be independently eliminated. Several attempts to separate tension and the potential change have met with apparent success particularly in the poisoned heart. These experiments have been reviewed recently by Einthoven and Hugenholtz l). They call attention to the great discrepancy between the energy necessary to move a galvanometer string and a muscle lever, and give some experiments, which were extended by Arbeiter(2), to show that if a sufficiently delicate and frictionless lever is employed, the tension and electrical potential in heart muscle decrease in a similar manner. In skeletal muscle it was shown by B i ed e rm ann (3) that if water rigor is produced in one end of a curarised sartorius, this end may be electrically stimulated and produce contraction in the normal end without itself contracting. The observation was confirmed by Engelmann (4) in the heart and later in skeletal muscle by Hiirtl (5) under conditions which exclude the possibility of spread of the stimulating current to the uninjured muscle. The only apparent objection to these experiments is that the recording apparatus may have been insufficiently sensitive to record a small amount of tension. More recently de Bo er(6) has shown action currents in the frogs heart treated with water at a time when it no longer registered contractions. He does not accept this as evidence of dissociation, however, as the swelling of the heart had caused a shortening to the systolic length and contraction could not be visible on account of the shortening already present. This, in effect, is an admission that there was tension which was not recorded. The present investigation, undertaken at the suggestion of Prof. A. V. Hill, is concerned with the possibility of separating the production

The Action Potential in Fibers of Slow Conduction in Spinal Roots and Somatic Nerves.

The group of waves, alpha, beta, gamma and delta, hitherto described as constituting the conducted action potential of mixed somatic nerve 1 , 2 are confluent and are produced by groups of fibers conducting at rates ranging in round numbers, in the bullfrog, green frog (at room temperature) and dog (at body temperature), between 40 and 10, 35 and 8 and 80 and 30 m.p.s., respectively. Together they form what may be called the A elevation. When the record obtained from these nerves by the cathode ray oscillograph is continued through 200 to 300 σ, instead of stopping after 10-15σ as has been usual hitherto, and higher amplification, 100,000 instead of 8,000, is used, 2 additional and discrete elevations, which, like A, may be compound, appear in succession as the stimulation is raised to strengths far beyond those previously employed by us. The second, or elevation B travels at the rate of about 5 to 2 m.p.s. in mixed nerves of the bullfrog and green frog and 17 (20 in one case) to 11 m.p.s. in the dog, the rates in the contributing fibers ranging down to about 2 to 1 m.p.s. in the frog and to about 8 m.p.s in the dog. The third or C elevation is conducted at the rate of 0.7 to 0.5 in the frog and 1.5 to 0.8 m.p.s. in the dog, the rates in the slowest fibers ranging down to about 0.3 m.p.s. in the frog and to 0.5 m.p.s. in the dog. The 3 elevations, A, B and C, are propagated at such diverse rates that in less than 1 cm. of conduction they become quite clear one of the other, in this respect differing strikingly from the alpha-beta-gamma waves of A which are confluent at all distances of conduction.