PHYSIOLOGY OF MUSCLE TISSUE. 53 



The rigidity appears first 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 extremities. It disappears in practi- 

 caHy the same order. 



Chemic changes of a marked character accompany this rigidity. 

 The muscle becomes acid in reaction from the development of sarco- 

 lactic acid ; it gives off a large quantity of carbonic acid, and is 

 shortened and diminished in volume. 



The immediate cause of the rigidity appears to be a coagulation of 

 the myosinogen within the sarcolemma, with the subsequent formation 

 of myosin and muscle serum. In the early stages of coagulation 

 restitution is possible by the circulation of arterial blood through 

 the vessels. The final disappearance of this contraction is due to 

 the action of acids dissolving the myosin, and possibly to putrefactive 

 changes. 



Source of Muscular Energy. According to most experimenters, it 

 is certain that "normal muscle activity is not dependent on the meta- 

 bolism of nitrogenous materials, inasmuch as its chief end product, 

 urea, is not increased. The marked production of CO 2 points to the 

 combustion of some non-nitrogenous matter, e. g., glycogen, espe- 

 cially as this substance disappears during muscular activity. Muscles 

 wanting in glycogen are, nevertheless, capable of contracting for 

 some time. Moreover, there is no proof of the direct combustion of 

 glycogen or any other carbohydrate. It has been suggested by Her- 

 mann that the energy of a muscular contraction may be due to the 

 splitting and subsequent re-formation of a complex body belonging 

 neither to the carbohydrates nor to the fats, but to the albumins. 

 To this body the term inogen has been applied. This complex 

 molecule, the product of the metabolic activity of the muscle cell, 

 in undergoing decomposition would yield CO 2 , sarcolactic acid, and 

 a proteid residue resembling myosin. With the cessation of the 

 contraction, the muscle protoplasm recombines the proteid residue 

 with oxygen, carbohydrates, and fats, and again forms inogen. 



The phenomena of rigor mortis support such a view. At the mo- 

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

 muscle becomes acid, and myosin is formed. There is thus a close 

 analogy between the two processes ; in other words, a contraction is 

 a partial death of the muscle. As to what becomes of the myosin 

 formed during a contraction, nothing is known. It may be used in 

 the formation of new inogen. 



