CHEMICAL PHENOMENA OF MUSCULAR CONTRACTION 777 



Blood applied to the cross-section of a muscle first stimulates the 

 fibres with which it is in contact, and then renders them rigid. 

 But it is to be remembered that normally the blood does not come 

 into direct contact even with the sarcolemma, much less with its 

 contents. 



The effect of heat is of special interest. A skeletal muscle of 

 a frog, like the gastrocnemius, if dipped into physiological saline 

 solution at 40 or 41 C. goes into rigor at once; the frog's heart 

 requires a temperature 3 or 4 higher; the distended bulbus aortae 

 can withstand even a temperature of 48 for a short time. An 

 excised mammalian muscle passes into immediate rigor at 45 to 

 50. In heat rigor the reaction of the muscle becomes strongly 

 acid owing to the formation of lactic acid, and the evolution of 

 carbon dioxide is also increased. 



The total discharge of carbon dioxide in heat rigor induced at 40 

 amounts to 35 to 40 c.c. per 100 grammes of muscle. An additional 

 15 to 20 per cent, is obtained on heating to 75 C. to completely coagu- 

 late the proteins, and a further 15 to 20 per cent, on heating to about 

 100 C. When a muscle is scalded by being suddenly immersed in 

 boiling salt solution, lactic acid is not formed, but carbon dioxide to the 

 amount of 60 to 70 per cent, is discharged. An excised muscle kept in 

 oxygen for many hours, during which it has discharged several times 

 as much carbon dioxide as is ever liberated by heating, still yields the 

 normal discharge on heating whether to 40 C. or to 100 C. On the 

 other hand, previous survival in an anaerobic atmosphere (of nitrogen) 

 reduces greatly or abolishes the yield of carbon dioxide at 40 C., 

 although not that at 100 C., the sum of the carbon dioxide given off to 

 the atmosphere of nitrogen and that given off on heating to 100 C. 

 being about equal to the total amount which would have been dis- 

 charged by a freshly-excised muscle on heating first to 40 C. and then 

 to 100 C. If acid is added to a fresh muscle at about o C. even more 

 carbon dioxide is liberated than in heat rigor, while the yield of lactic 

 acid is, even after many hours, very little increased above the normal 

 amount for fresh resting muscle. When the acidified muscle after the 

 discharge of the carbon dioxide is now heated to 40 C., the yield of 

 lactic acid is increased, but only traces of carbon dioxide are given off. 



From these and similar observations, Fletcher concludes that the 

 carbon dioxide discharged during heat rigor at 40 C. is pre-existent 

 carbon dioxide set free from carbonates or other compounds by 

 the lactic acid known to be produced in heat rigor. The carbon 

 dioxide discharged at 75 and 100 C. he regards as held by 

 muscle colloids or in combination with amino-acid groups. These 

 results tend to discredit the ' inogen ' theory (p. 270), with its 

 assumption that ' intramolecular oxygen ' is stored away in the 

 muscle, which was largely based upon erroneous observations on 

 the discharge of carbon dioxide from heated muscles. According 

 to this theory, carbon dioxide and lactic acid were supposed to arise 

 from a common precursor into which oxygen had been previously 

 introduced. 



