458 THE HUMAN BODY. 



which it would have given off in two stages, if first worked 

 and then sent into rigor. The muscle must, therefore, con- 

 tain a certain store of a carbon-dioxide-yielding body, and 

 the decomposition of this is associated with the occurrence 

 both of muscular activity and death stiffening. Similar 

 things are true of the acid simultaneously developed; the 

 muscle when it works produces some sarcolactic acid, and 

 when thrown into rigor mortis still more. No increase of 

 urea or kreatin or any similar product of nitrogenous de- 

 composition is found in a worked muscle when compared 

 with a rested one, but the total carbohydrates are rather less 

 in the former. These facts make it clear that muscular work 

 is not done at the expense of proteid oxidation; and we have 

 already seen (Chap. XXVI) that the oxygen a muscle uses in 

 contracting is not taken up by it at the time it is used, since 

 a muscle containing no oxygen will still contract in a vacuum 

 and form carbon dioxide. It is probable that the chemical 

 phenomena occurring in contraction and rigor are essentially 

 the same; the death stiffening results when they occur to an 

 extreme degree. Provisionally one may explain the facts as 

 follows: A muscle in the Body takes up from the blood, 

 oxygen, proteids, and non-nitrogenous (carbohydrate or fatty) 

 substances. These it builds up into a highly complex and 

 very unstable compound, comparable, for example, to nitro- 

 glycerine. When the muscle is stimulated this falls down 

 into simpler substances in which stronger affinities are satis- 

 fied; among these are carbon dioxide and sarcolactic acid and 

 a proteid (myosinogen). The energy liberated is thus in- 

 dependent of any simultaneous taking up of oxygen; the 

 amount possible depends only on how much of the decom- 

 posable body existed in the muscle. Under natural condi- 

 tions the carbon dioxide is carried off in the blood and per- 

 haps the sarcolactic acid also, the latter to be elsewhere 

 oxidized further to form water and more carbon dioxide. 

 The myosinogen remains in the muscle-fibre and is combined 

 with more oxygen, and with compounds of carbon and hydrogen 

 taken from the blood, and built up into the unstable energy- 

 yielding body again; no increased quantity of nitrogenous 

 material, under ordinary circumstances, leaves the working 

 muscle. If, however, the blood-supply be deficient, myosin 

 forms from myosinogen and clots (Chap. IX) before this 

 restitution takes place, and cannot be directly rebuilt into 



