GENERAL PHYSIOLOGY OF MUSCULAR TISSUE. 47 



in the muscles of the abdomen and upper extremities; finally in the trunk and 

 lower extremities. It disappears in practically the same order. 



Chemic changes of a marked character accompany this rigidity. The 

 muscle becomes acid in reaction from the development of sarcolactic acid; 

 it gives off a large quantity of carbonic acid, and is shortened and dimin- 

 ished 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 disap- 

 pearance of this contraction is due to the action of acids dissolving the myosin, 

 and possibly to putrefactive changes. 



Source of Muscle Energy. According to most experimenters, it is cer- 

 tain that normal muscle activity is not dependent on the metabolism of nitrog- 

 enous materials, inasmuch as its chief end product, urea, is not increased. 

 The marked production of CO 2 points to the decomposition of some unstable 

 compound of a carbohydrate character, rich in carbon and hydrogen. It 

 has been suggested that glycogen furnishes the energy after it has been 

 transformed into sugar. Muscles wanting in glycogen are, nevertheless, 

 capable of contracting for some time. It has been suggested by Hermann 

 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 carbo- 

 hydrates 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 protein residue resembling myosin. With the 

 cessation of the contraction, the muscle protoplasm recombines the 

 protein residue with oxygen, carbohydrates, and fats, and again forms 

 inogen. 



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

 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. 



The Physical Properties of Muscle Tissue. The consistency of muscle 

 tissue varies considerably, according to the different states of the muscle. 

 In a state of tension it is hard and resistant; when free from tension, it is 

 soft and fluctuating, whether the muscle is contracting or resting. Tension 



