58 ANIMAL PHYSIOLOGY. 



36. Some time after death, at a period said to vary from 

 ten minutes to eighteen hours, or longer, a state of rigidity 

 of the muscles sets in, termed cadaveric rigidity or rigor 

 mortis. It begins in the face, and extends successively to 

 the trunk and upper and lower limbs, and disappears from 

 the parts in the same order, after lasting for a period varying 

 from a few hours to several days, and longest in those 

 instances in which it has set in latest. It is longest delayed 

 and most marked in strong subjects who have been cut off 

 in full vigour. It never sets in till after the disappearance 

 of irritability, and that circumstance is sufficient to show 

 that it is not, as has sometimes been supposed, a contraction 

 of the muscles. Rigor mortis is often so intense as to render 

 it impossible to alter the attitude of the limbs without tear- 

 ing the muscles or damaging the bones; but it never alters 

 the position in which the body is lying; for example, it does 

 not raise the jaw when it has dropped in death; and in this 

 it differs obviously from muscular contraction. The use of 

 muscles is to produce movement by their contraction; and 

 when two opposing groups are both made spasmodically rigid, 

 as may happen in tetanus, the stronger overcomes the other. 

 But so far from this being the case in rigor mortis, it is known 

 to every undertaker that a body stiffens in whatever position 

 it is placed in. No doubt some apparently well authenticated 

 stories are on record of movements of the limbs taking place 

 in persons who had died of yellow fever; but, however difficult 

 such cases may be to account for, the very circumstance that 

 the movements were neither spasms nor mere twitchings, but 

 of a combined description, shows that they were not a variety 

 of rigor mortis, and did not originate in the muscular texture, 

 but in the nerves; and the explanation of them must be 

 sought in some irritation of the central nervous system, 

 probably by a product of decomposition, before irritability 

 had ceased in the muscles. It appears, then, that rigor mortis 

 produces no change in the length of the muscles ; and there 

 seems good reason to accept the hypothesis that it is a 

 phenomenon due to chemical change which coagulates the 

 myosin; but it must be admitted that we are not yet pro- 

 perly acquainted with the chemical distinctions of muscle 

 prior to, during, and subsequent to rigor mortis. 



