160 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Conditions which Influence the Development of Rigor. — Ordinarily on the 

 deatli of the body the muscle enters into rigor slowly — the muscle-fibres are 

 involved one after the other, and through the gradual contraction and harden- 

 ing of the antagonistic muscles the joints become fixed and the body acquires 

 the rigidity which we associate with death. Rigor usually affects the different 

 parts of the body in a regular order, from above downward, the jaw, neck, 

 trunk, arms, and legs being influenced one after the other. The position taken 

 by the body is generally determined by the weight of the parts and the rela- 

 tive strength of the contractions of the muscles. 



The time required for the appearance of rigor is very variable. It is deter- 

 mined in part by the nature of the muscle, its condition at the moment of 

 death, and the temperature to which it is subjected. The muscles of warm- 

 blooded animals enter into rigor more quickly than those of cold-blooded 

 animals; of the warm-blooded animals, pale muscles more quickly than red, 

 and the flexors before the extensors ; of the cold-blooded animals, frog's muscles 

 more quickly than those of the turtle. In general, the more active the muscle 

 protoplasm, the more rapid are the chemical changes which it undergoes, and 

 amongst these the coagulation of rigor mortis. 



The condition of the muscle plays a very important part in determining the 

 onset of rigor. If the muscles are strong and vigorous and death of the body 

 has come suddenly, rigor develops slowly ; if the muscles have been enfeebled 

 by disease or fatigued by great exertion shortly before death, it comes rapidly. 

 In the case of wasting diseases rigor comes quickly, is poorly developed, and 

 passes oil" quickly ; when the muscles are fatigued at the time of death, as in 

 the case of a hunted animal, it comes quickly. We hear of soldiers found dead 

 on the field of battle grasping the sword, as if the muscular contractions of life 

 had been continued by the contractions of death. In the case of certain dis- 

 eases of the spinal cord and brain, too, rigor may come so rapidly that the 

 limbs may maintain the position which they had at the time of death, "cata- 

 leptic rigor," as it has been called. The coming on of rigor is particularly 

 striking in the case of diseases which, like cholera, are accompanied by violent 

 muscular cramps and lead to a rapid death. It is not uncommon, in such 

 cases, for the contractions of rigor to cause movements which may mislead a 

 watcher into supposing the dead man to be still alive. This idea is favored by 

 the fact that the body may remain warm, owing to the heat which is produced 

 in the muscles as a result of the chemical changes occurring during rigor. 

 The post-mortem muscular contractions and the rise of temperature observed 

 in such cases arc only excessive manifestations of what always occurs on the 

 death of the muscle. The movements are probably due, in part, to the rapidity 

 with which the muscles contract in rigor, and in part to the fact that the 

 antagonistic muscles are not affected at the same time to the same degree. 

 Whether the contractions are partly excited by changes accompanying the 

 death of the motor nerve-cells in the central nervous system is uncertain, but 

 Qol impossible. Muscle- are still able to respond by contractions to stimuli 

 coming to them through the nerve, even after rigor has become quite pro- 



