GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 75 



points to the disruption of some carbohydrate, perhaps sugar, derived from 

 the stored glycogen and the oxidation of the intermediate products to carbon 

 dioxid and water. The oxidizable compound appears to be lactic acid. 

 For if the muscle be made to contract in an atmosphere deficient in oxygen, 

 the amount of lactic acid produced is relatively large and the amount of 

 carbon dioxid relatively small. If the surrounding atmosphere be rich 

 in oxygen, the reverse conditions obtain. Under physiological conditions, 

 when the muscle is supplied with blood containing its customary percentage 

 of oxygen, it is probable that the products set free by the disruption of the 

 sugar molecule are rapidly oxidized to CO 2 and H 2 O, with the liberation of 

 their contained energy. But the fact that muscle will contract in an atmos- 

 phere free of oxygen, that no free oxygen can be obtained from muscle, 

 would support the idea that the mechanism is one of decomposition. Her- 

 mann 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 

 dioxid, 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 0.001 C. to 0.005 C. an( ^ after tetanization an 

 increase of from o. 14 C. to o. 18 C. 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, 



