GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 77 



cause, such as chronic disease or defective blood-supply, the rigidity appears 

 promptly but is of short duration. After death from acute diseases it is apt 

 to be delayed, but will continue for a longer period. The rigidity first 

 appears in the muscles of the lower jaw and neck; next in the muscles 

 of the abdomen and upper extremities; finally in the trunk and lower ex- 

 tremities. It disappears in practically the same order. Chemic changes 

 of a marked character accompany this process. The muscle becomes acid 

 in reaction from the development of sarcolactic acid and there is a large 

 increase in the amount of carbon dioxid given off. The immediate cause 

 of the rigidity appears to be coagulation of the myosin and myogen within 

 the sarcolemma with the formation of two insoluble proteins, myosin fibrin 

 and myogen fibrin. . In the early stages of the coagulation restitution is 

 possible by the circulation of arterial blood through the vessels. The final 

 disappearance of this post-mortem rigidity is due probably to the action of 

 acids which render the myosin and myogen fibrins soluble, and possibly 

 to the action of various microorganisms which give rise to putrefactive 



changes. 



Source of the Muscle Energy. The nature of the materials which are 

 the immediate sources of the muscle energy has been the subject of much 

 discussion. The absence of any noticeable increase in the quantity of 

 urea or other nitrogen-holding compounds excreted renders ^ it probable 

 that the energy does not come from the metabolism of protein ^materials. 

 The marked production of carbon, dioxid and sarcolactic acid points to the 

 decomposition of some unstable compound, of a carbohydrate character, 

 rich in carbon and oxygen. As the result of many investigations it has come 

 to be believed that glycogen is the compound which furnishes the energy 

 under physiologic conditions, inasmuch as this substance, generally present in 

 muscle, disappears during activity. A muscle which has been tetanized 

 contains less glycogen than the corresponding muscle at rest. A muscle 

 which has been separated from the nervous system by division of its nerves 

 and thus prevented from contracting accumulates glycogen. Bunge 

 of the opinion that though the carbohydrates are the main, they are not 

 the only sources of muscle energy. If there is a deficiency or absence of 

 carbohydrate food, the muscle will utilize fat and protein, for experiment 

 has shown that the available glycogen is entirely consumed by the second < 

 third day. The mechanism by which the energy is liberated, whether 

 by direct oxidation or decomposition is uncertain. The general teen 

 experimental investigation points to the disruption of some carbohydrate, 

 perhaps glucose, derived from the stored glycogen and the oxidation o 

 intermediate products to carbon dioxid and water. The oxidizable com- 

 pound appears to be lactic acid. For if the muscle be made to co: 

 in an atmosphere deficient in oxygen, the amount of lactic acid produced 

 is relatively large and the amount of carbon dioxid relatively i 

 the surrounding atmosphere be rich in oxygen, the reverse, conditions 

 obtain. Under physiological conditions, when the muscle i supplied 

 with blood containing its customary percentage of oxygen i 

 that the products set free by the disruption of the sugar molecule are raj 

 oxidized to C0 2 and H 2 O, with the liberation of their Contained energy. 

 But the fact that muscle will contract in an atmosphere free < 

 that no free oxygen can be obtained from muscle, would support 



