Volume changes in frog muscle during contraction

The variation in volume when a muscle contracts was the subject of much discussion towards the end of the 17th century, and more recently by Fulton (1926) and by Ernst (1958). Many scholars expected an increase in volume as the vital spirits moved from the nerve into the muscle and induced activation: but Swammerdam (ca. 1660) experimented with an isolated muscle contained in a jar with a fine-bore tube attached and in fact observed a slight decrease in volume. Ernst (1925) first demonstrated the decrease with certainty and set the stage for many investigations of volume change in frog striated muscle. Meyerhof & Hartmann (1934) showed that the volume decrease during tetanic contraction parallelled the development of tension, and that a further decrease accompanied maintenance of the tension. They also made precise studies of the slow changes in volume which occur following mechanical activity. These were related quantitatively to the formation of lactic acid under anaerobic conditions and to the break-down of creatine phosphate in an iodoacetate-poisoned muscle. Fischer (1941), on the other hand, reported the occurrence of a volume increase as well as a decrease during contraction, but this was not confirmed by Ernst. All the authors found a volume decrease of about 0-002 % of the muscle volume during a short tetanus, but the response of the apparatus was too slow to record the precise time relationships of the change during contraction. A tetanus was necessary in order to obtain a change large enough to record; the muscles used were almost always large gastrocnemii and usually several muscles were necessary. Hill (1948) has criticized this choice: the fibres in the gastrocnemius muscle do not run parallel through the length of the muscle but instead are arranged at an angle to the axis of the muscle, so that during contraction a portion of the muscle tension would be directed at right angles to the axis of the muscle, thus producing an internal pressure. This was demonstrated by Hill and can also be substantiated by the observation in mammals that during