668 A MANUAL OF PHYSIOLOGY 



hydrogen atom is replaced, say, by sodium or potassium) reddens blue 

 litmus, while diphosphate (where two hydrogen atoms are replaced) 

 turns red litmus blue. Litmoid (lacmoid) differs from litmus in not 

 being affected by monophosphates. Diphosphates turn red litmoid 

 blue, and so does fresh muscle, which has no effect on blue litmoid. 

 A cross-section of fresh muscle is about neutral (sometimes faintly 

 acid) to turmeric paper, which is turned yellow by monophosphates. 

 A muscle which has entered into rigor or has been fatigued by pro- 

 longed stimulation is distinctly acid to blue litmus and to brown 

 turmeric, reddening the former and turning the latter yellow, but 

 does not affect blue litmoid. 



Perfectly fresh resting muscle excised with avoidance of all 

 unnecessary manipulation contains very little lactic acid (as 

 little as 0-02 per cent, expressed as zinc lactate). Mechanical 

 injury, heating, and chemical irritation cause a marked increase 

 in the amount. Under anaerobic conditions in an atmosphere 

 of hydrogen, for instance lactic acid is spontaneously developed 

 in the resting muscle so long as irritability persists, but not 

 longer. In air, which for even small excised muscles corresponds 

 to a partial asphyxia, there is a small increase in the lactic acid, 

 but its production is very slow in comparison with that in the 

 hydrogen atmosphere. In pure oxygen not only is there no 

 accumulation of lactic acid for a long time after excision, but a 

 portion of the amount originally present in the resting excised 

 muscle disappears. The same is true of the lactic acid formed 

 in a muscle fatigued by stimulation when it is afterwards placed 

 in an atmosphere of pure oxygen. There is no doubt that the 

 production of lactic acid in functional activity and its trans- 

 formation into other substances are processes that go on also 

 in the muscles of the intact body. The formation of the acid in 

 the excised muscle, far from being a sign of death, is an index of 

 the ' survival ' of a process by which it is normally formed, as 

 the accumulation of it is an index of the crippling, in the absence 

 of oxygen, of a mechanism by which it is normally trans- 

 formed. 



The lactic acid which accumulates in the excised muscle in 

 rigor and activity does not remain free, since blue litmoid paper 

 is not reddened as it would be by free lactic acid. It causes a 

 repartition of the bases at the expense of the sodium carbonate 

 and disodium phosphate, the latter being changed into mono- 

 phosphate, which, in part at least, accounts for the acid reaction 

 to turmeric (Rohmann). It is of great interest that this oxidative 

 transformation of lactic acid only occurs in muscle whose struc- 

 ture is so far preserved that its irritability is not lost. In minced 

 or triturated muscle it does not take place. 



Glycogen is the one solid constituent of muscle which has 

 been definitely proved to diminish during activity. It accumu- 

 lates in a resting muscle, especially in a muscle whose motor 



