MUSCLE IN RIGOR MORTIS 461 



nervous system. Such motor impulses may arise through reflexes, through 

 automatic activity of the nerve center, or by higher cerebral origin associated 

 with conscious psychic effort. In either case the apparatus consists of one 

 or more central neurones, an anterior-horn motor cell, and the muscle 

 itself. Conscious or voluntary effort may be taken as a type. 



Simple contractions are possible to human muscles, but undoubtedly 

 tetanic contractions are the rule. If one holds the arm out at right angles to the 

 trunk, the movement requires the continuous or tetantic contraction of the 

 deltoid and the series of extensor muscles. If the arm is retained in the 

 extended position long enough, extreme fatigue is felt and presently one can 

 no longer maintain the position. Yet, if the muscles involved are immediately 

 stimulated directly with an electric current, they contract, showing that such 

 exhaustion as exists is not wholly due to the muscle. 



Mosso's ergograph was devised for the specific purpose of studying the 

 character of fatigue of voluntary effort. This apparatus is adapted to the 

 study of the fatigue of the flexors of the middle finger, or, in the newer in- 

 strument devised by Storey, to the abductor of the index finger. Numerous 

 studies have shown, apparently, that the fatigue of voluntary effort involves, 

 first, the nervous apparatus and, later, the muscle; that the muscle still retains 

 a considerable reserve of energy \vhen the apparatus as a whole is exhausted. 



Muscle in Rigor Mortis. After the muscles of the dead body have 

 lost their irritability or capability of being excited to contraction by the ap- 

 plication of a stimulus, they spontaneously pass into a state of contraction 

 apparently identical in effect with that which ensues during life. It affects all 

 the muscles of the body, and, when external circumstances do not. prevent it, 

 commonly fixes the limbs in that which is their natural posture of equilibrium 

 or rest. From the simultaneous contraction of all the muscles of the trunk, 

 a general stiffening of the body is produced, which constitutes the rigor 

 mortis or post-mortem rigidity. 



When this condition has set in, the muscle becomes acid in reaction (due to 

 development of sarcolactic acid), gives off carbonic acid in great excess, 

 diminishes in 'volume slightly, becomes shortened and opaque, its substance sets 

 in a firm coagulatio. Rigor comes on much more rapidly after muscular 

 activity, and is hastened by warmth. 



The immediate cause of rigor seems to be a chemical one, namely, the 

 coagulation of the muscle plasma. We may distinguish three main stages; 

 i. Gradual coagulation. 2. Contraction of coagulated muscle clot (myosin), 

 and 3, squeezing out of muscle serum. During the first stage, restoration is 

 possible, by the circulation of arterial blood through the muscles; 

 and even when the second stage has set in, vitality may be restored 

 by dissolving the coagulum of the muscle in salt solution, and passing arterial 

 blood through the vessels. After the second stage is advanced, recovery is 

 impossible. 



