78 TEXT-BOOK OF PHYSIOLOGY 



that the .mechanism is one of decomposition. Hermann suggests that 

 the energy of a contraction is liberated by the splitting and subsequent 

 re-formation of a complex body belonging neither to the carbohydrates 

 nor fats, but to the proteins to this hypothetic body the term inogen 

 is given. This complex molecule, the product of the nutritive activity 

 of the muscle-cell in undergoing decomposition, would yield carbon di- 

 oxid, sarcolactic acid, and a protein residue resembling myosin. On the 

 cessation of the contraction the muscle-cell recombines the protein residue 

 with oxygen, carbohydrates, and fats, and again forms the energy-holding 

 compound, inogen. The phenomena of rigor mortis support this view. 

 At the moment of this contraction the muscle gives off CO 2 in large amount, 

 develops sarcolactic acid and myosin. There is thus a close analogy be- 

 tween the two processes; in other words, a contraction is a partial death of 

 the muscle. If this view is correct, then the oxygen is required mainly for 

 heat production through oxidation processes. 



THERMIC PHENOMENA 



The potential energy liberated in a muscle on the arrival and subsequent 

 action of a nerve impulse, manifests itself partly as heat and partly as 

 mechanic motion or a change of shape of the muscle. Though heat pro- 

 duction is taking place even during the passive condition, it is largely in- 

 creased by muscle activity. The amount of heat produced will vary however 

 with a variety of conditions, as strength of stimulus, tension, work done, etc. 



Stimulus. It has been experimentally determined that the skeletal 

 muscle of the frog, the gastrocnemius, shows after a single contraction a rise 

 in temperature of from o.ooiC. to o.oo5C. and after tetanization an 

 increase of from o.i4C. to o.i8C. It has also been shown that an increase 

 in the strength of the stimulus from a minimal to a maximal value increases 

 the amount of heat liberated. This is the direct result of increased chemic 

 change naturally following increased stimulation. 



Tension. The greater the tension of a muscle, the greater, other condi- 

 tions being the same, is the amount of heat liberated. If the muscle is 

 securely fastened at both extremities so that shortening is practically im- 

 possible during the stimulation, the maximum of heat production is reached. 

 In the tetanic state the great increase in temperature is due to the ten- 

 sion of antagonistic and strongly contracted muscles. In both instances, 

 mechanic motion being prevented, the liberated energy is transformed into 

 heat. 



4 Mechanic Work. If the muscle is permitted to shorten and raise a 

 weight, some of the energy liberated takes the form of mechanic motion. If 

 the weight is removed at the height of the contraction, external work is 

 accomplished. The greater the weight raised, within limits, the greater is 

 the percentage of energy which takes the direction of mechanic motion. The 

 percentage of the total energy liberated which is thus utilized, has been 

 estimated at from 25 to 40 per cent. In accordance with the law of the con- 

 servation of energy, the heat produced, stated in calories, plus the energy 

 required in the raising of the weight, expressed in kilogrammeters of work, 

 must equal the, potential energy transformed. 

 y A muscle during a tetanic contraction of short duration accomplishes 



