456 MUSCLE PHENOMENA. 



for instance, those of the leg than those of the arm. The same 

 difference is seen in the corresponding muscles of different animals. 



5. Effect of Drugs. The effect of drugs upon muscular contrac- 

 tion is well illustrated by injecting veratrin under the skin of a 

 frog : the principal characteristic of the muscle-curve produced 

 being the extreme prolongation of the period of relaxation 

 (Fig. 264). 



Rigor Mortis. It has already been stated (p. 62) that the 

 coagulation of the muscle-plasma is the cause of rigor mortis or 

 cadaveric rigidity, in which the muscle becomes opaque and stiff, 

 and loses its elasticity and extensibility ; at the same time it 

 becomes warmer and acid in reaction. Rigor usually appears in 

 from one hour to five hours after death, although this is subject 

 to great variation, coming on more rapidly in muscles that are 

 feeble than in those that are strong and vigorous. Thus in per- 

 sons who have been in good health, dying suddenly, it comes on 

 slowly ; while when death occurs after protracted illness it comes 

 on quickly, and remains but a short time. Animals which have 

 been hunted, and whose muscles are consequently exhausted by 

 fatigue, are the subjects of early rigor mortis. There are, how- 

 ever, instances in which rigor has come on very early in those 

 who were presumably in health at the time, although it is pos- 

 sible that these were not exceptions, and that the cause of the 

 early appearance was due to muscular exhaustion ; as, for instance, 

 soldiers killed in battle being found with one eye closed and the 

 other open in the act of taking aim. It has been said that after 

 death from lightning or in the heat of passion, rigor mortis is 

 entirely absent ; but it is more than probable that in such cases 

 it comes on early and disappears without having been ob- 

 served. 



Rigor mortis, as a rule, is first observed in the necjv and lower 

 jaw, then in the upper, and later in the lower extremities, passing 

 off in the same order. There are, however, exceptions to this. 

 It may remain for from one to six days. 



Little is known about rigor mortis of involuntary muscle, 

 although this condition has been seen in the heart, stomach, and 

 uterus. 



Muscular Tone. If a relaxed muscle is divided, the two ends 

 separate i. e., each portion of the divided muscle contracts, so that 

 even in a so-called relaxed muscle this is in a state of tonic con- 

 traction, and this condition is muscular tone or muscular tonus. 

 The advantage which accrues from this is that when the muscles 

 are called upon to perform any work they are already in a posi- 

 tion to effect results quickly, which would not be the case if it 

 were necessary to bring them from a state of complete relaxa- 

 tion to one of effective contraction. It is as if one desired to 



