778 THE PHYSIOLOGY OF THE CONTRACTILE TISSUES 



The production of heat in heat rigor is also of great interest. 

 Hill has shown that it amounts to from 0-6 to i-o gramme calorie 

 per gramme of muscle. Of this no more than 0-05 calorie can be 

 due to the heat of neutralization of lactic acid by the sodium 

 bicarbonate in the muscle, with which it reacts as soon as it is 

 liberated. The rest of the heat is associated with the chemical 

 reaction by which lactic acid is formed from its precursor, a reaction 

 which, there is every reason to believe, is the same as that which 

 occurs in muscular contraction. The heat production can only 

 be due in very slight degree to the physical alteration (clotting or 

 precipitation) of the muscle proteins. 



The so-called rigor caused by water, which is not a true rigor, 

 causes no increase in the carbon dioxide given off. Chloroform, 

 on the other hand, produces a marked increase in the carbon 

 dioxide production, and this is evidently related to its action in 

 hastening the onset of rigor. Rigor mortis is to some extent in- 

 fluenced by the nervous system, for section of its nerves retards 

 the onset of rigor in the muscles of a limb. Ante-mortem stimula- 

 tion of the peripheral ends of the vagi, even with currents too weak 

 to cause a perceptible effect upon the heart-beats, prolongs the 

 period of spontaneous contraction and the irritability of the ven- 

 tricles after death, and retards the onset of rigor (Joseph and 

 Meltzer). Cold rigor is obtained when frog's muscles are cooled 

 to 15 C. The muscles remain perfectly translucent. They 

 do not recover their irritability on thawing, but if cooled only to 

 7 C. they recover (Folin). 



In a human body rigor generally appears not earlier than an 

 hour, and not later than four or five hours, after death. In ex- 

 ceptional cases, however, it may come on at once, and the annals 

 of war and crime contain instances where a man has been found 

 after death still holding with a firm grip the weapon with which 

 he had fought, or which had been thrust into his hand by his 

 murderer (so-called cataleptic rigor). It is related that after 

 one of the battles of the American Revolutionary War some of the 

 dead were found with one eye open and the other closed as in the 

 act of taking aim. A high temperature favours a rapid onset; a 

 body wrapped up in bed will, other things being equal, become rigid 

 sooner than a body lying stripped in a field. Muscular exhaustion, 

 as we have said, is another favouring condition: hunted animals 

 and the victims of wasting diseases go quickly into rigor. It is 

 a rule, but not an invariable one, that rigor, when it comes on 

 quickly, is short, and lasts longer when it comes on late. All the 

 muscles of the body do not stiffen at the same time; the order 

 is usually from above downwards, beginning at the jaws and neck, 

 then reaching the arms, and finally the legs. After two or three 

 days the rigor disappears in the same order. The position of the 



