526 MUSCLE-NERVE PHYSIOLOGY 



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 when the apparatus as a whole is 

 exhausted. 



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

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

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

 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 postmortem 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 coagulation. Rigor mortis comes on much more rapidly in death 

 after muscular activity, and is hastened by warmth. 



The immediate cause of rigor mortis 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 the 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 dis- 

 solving the coagulum of the muscle by salt solution and by passing arterial 

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

 impossible. 



It has been noticed that the relaxation in muscles after rigor sometimes 

 occurs too quickly to be caused by putrefaction. The suggestion that in 

 such cases the relaxation is due to a ferment action is very plausible. 

 Subjecting. fresh muscle to the action of heat (50 to 60 C.) or immersing 

 it in distilled water causes a similar coagulation to that of rigor mortis. 

 The former is known as heat rigor, and the latter as water rigor. 



The muscles are not affected simultaneously by rigor mortis. It affects 

 the neck and lower jaw first; next, the upper extremities, extending from 

 above downward; and, lastly, reaches the lower limbs. In some rare in- 

 stances only it affects the lower extremities before or simultaneously with 

 the upper extremities. It usually ceases in the order in which it begins: 

 first at the head, then in the upper extremities, and lastly in the lower ex- 

 tremities. It never ordinarily commences earlier than ten minutes, and 

 never later than seven hours after death; and its duration is greater in pro- 



