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 myogeh 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. 



The Source of the Energy and the Nature of the Muscle Contraction. 

 The passage of a nerve impulse into a muscle, together with its subsequent 

 action, calls forth a pulsation, which is attended with the production of 

 lactic acid, carbon dioxid and water and the liberation of heat. These 

 phenomena would indicate that some compound had undergone an oxida- 

 tion in whole or in part at least. The exact chemic character of the 

 compound that has undergone oxidation has been a subject of much 

 discussion. The absence of any increase in the urea or other nitrogen- 

 holding bodies eliminated, excluded proteins. The marked production 

 of lactic acid and carbon dioxid led to the conclusion that the compound 

 in question, by reason of its chemic relations, was glycogen or glucose, 

 as the former, always present in muscle diminishes during activity, and 

 increases during rest. It was supposed that the glucose derived from the 

 blood or from the transformation of glycogen, was first converted into 

 lactic acid which compound was then directly oxidized to carbon dioxid 

 and water and the liberation of its contained energy. The view that 

 lactic acid is the oxidizable compound is supported by the fact that when 

 a muscle is made to contract in an atmosphere deficient in oxygen, the 

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

 carbon dioxid produced relatively small, while if the atmosphere is rich 

 in oxygen, the reverse conditions obtain. It is conceivable however 

 that if the supply of carbohydrates be limited, fat may be utilized. The 

 mechanism by which the nerve impulse initiates the transformation of 

 the sugar is unknown. 



Whatever the compound may be that yields the energy, the problem 

 requiring solution is, how do the chemic changes and the concomitant 

 liberation of energy cause the muscle to contract. Many theories having 

 reference to the elasticity, the electric, chemic and anatomic features of 

 the muscles have been advanced and for a time have found acceptance. 



Englemann advanced an explanation based on the structure of the 

 muscle which has had wide acceptance. It was observed that at the time 

 of the contraction, both the dim and light bands composing the fibrillae, 

 consisting respectively of doubly refracting and singly refracting material, 



