GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 87 



with muscujar contraction, the blood-vessels become widely dilated, 

 leading to a large increase in the blood-supply and a rapid removal 

 of the products of decomposition. 



Rigor Mortis. A short time after death the muscles pass into a 

 condition of extreme rigidity or contraction which lasts from one to 

 five days. In this state they offer great resistance to extension. 

 Their tonicity disappears, their cohesion diminishes, and their irri- 

 tability ceases. The time of the appearance of this postmortem 

 rigidity varies from a quarter of an hour to seven hours. Its onset 

 and duration are influenced .by the condition of the muscle irrita- 

 bility at the time of death. / When the irritability is impaired from 

 any cause, such as chroakLcjisease or defective blood-supply, the 

 rigidity appears promptly but j oL&hart duration! . After death from 

 acute diseases it is apt to be delayed, but will continue for a longer 

 period. The rigidity jjr^t appears in the muscles of the l^wer iaw 

 and nsck: next in the muscles of the abdomen and upper extrejnities ; 

 finally in the trunk and lower extremities. ~It disappears irTprac- 

 tically 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 gause of the 

 rigidity appears to be coagulation of the myosinogen withnTthe sarco- 

 lemma with the formation of an insoluble proteid, myosin/vln the 

 early stages of the coagulation restitution is possible by the circula- 

 tion of arterial blood through the vessels. The final disappearance 

 of this postmortem rigidity is due to the action of acids which render 

 the myosin soluble, and possibly to the action of various micro- 

 organisms which give rise to putrefactive changes. 



Source of the Muscle Energy. Notwithstanding many in- 

 vestigations, the nature of the materials which are the immediate 

 source of the muscle energy is not known. The absence of any notice- 

 able increase in the quantity of urea or other nitrogen-holding com- 

 pounds excreted renders it probable that the energy does not come 

 from the metabolism of proteid 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. It has been suggested that glycogen furnishes the 

 energy, inasmuch as this substance, generally present in muscle, dis- 

 appears 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 glycogenA Bunge 



is of the opinion that though the rarhnViyHratps flrgjfopjrmin. theyjye 

 not the only sources of muscle energy. If there is a deficiency or 

 absence of carbohydrate foocl, lEe 'muscle will utilize fat and pro- 



