THE CHEMISTRY OF MUSCLE 91 



like increases are frequently observed at the beginning of a series of 

 contractions of either striated, non-striated or cardiac muscle when 

 stimulated with induction shocks of constant strength. According 

 to Lee, this initial "Treppe" is due to a sudden increase in the 

 irritability of the muscle, following the early production and accumula- 

 tion of small quantities of the fatigue substances. It may be accepted 

 as proven that the seat of this excitation is the myoplasm and not the 

 neuroplasm, because these increases also develop in curarized muscles 

 and in muscles which have suffered a degeneration of their nervous 

 elements. 



The Chemistry of Rigor Mortis. The condition of death rigor is 

 characterized by a rigidity of the musculature which makes its appear- 

 ance very shortly after the general functions of the body have ceased. 

 It manifests itself by a loss of the irritability and contractility of the 

 myoplasm. The muscle becomes opaque, stiff, and firm to the touch 

 and, unless its tendency to shorten is opposed by a slight counterforce, 

 is prone to assume a state of very slight contraction. 



Under ordinary conditions, rigor mortis affects the different muscles 

 in a definite sequence from above downward, beginning with those of 

 the jaws and neck and finally involving those of the trunk, arms and 

 legs. It is also noted that these muscles are affected gradually, i.e., 

 fiber after fiber and not simultaneously throughout their substance. 

 The degree of their shortening is determined by the weight of the part 

 moved by them and the force opposing this tendency. Thus, the 

 simultaneous stiffening of the flexors and extensors finally gives rise 

 to a fixed position of the extremities so that the joints become im- 

 movable, but inasmuch as these muscles are antagonistically placed, 

 practically no shortening results. This fact that the muscle in rigor 

 retains its normal form almost completely, may be more plastically 

 portrayed by cutting the tendons of either the flexors or extensors of 

 the foot at death. It will then be found that the subsequent rigor 

 of the opposing muscles does not materially change the position of the 

 foot. 



The time required for the development of rigor mortis is very 

 variable. Most generally it makes its appearance in from 1 to 5 hours, 

 but in some cases it may begin as early as 10 minutes after death. A 

 delay of from 20 to 24 hours is not unusual. Under certain conditions 

 it may develop almost instantaneously, giving rise to the so-called 

 cataleptic rigor. Thus, it is narrated that soldiers have been found 

 in rigor with the gun at their shoulders and with one eye open and the 

 other closed as in the act of taking aim. In all these and similar cases, 

 the central nervous system was found to have been seriously lacerated. 

 The duration of rigor mortis is also very uncertain, because it may 

 last anywhere from a few hours to a few days, or even a week. A 

 quick onset, however, usually suggests a short duration. Forced 

 movement of the parts frequently tends to bring on relaxation. 



The factors which may be held responsible for this variation in the 



