CHEMICAL PHENOMENA OF MUSCULAR CONTRACTION 7&> 



are associated with the activity of the muscular tissue, but does 

 not of itself prove that the final steps of the oxidation occur in the 

 muscles themselves. This has been demonstrated, however, by 

 observations on isolated muscles. When well supplied with 

 oxygen, these, in addition to the stock of carbon dioxide in solution, 

 in the form of carbonates and in other combinations, which they 

 possess at the moment of isolation, continue to produce carbon 

 dioxide, and this production is markedly increased by stimulation. 

 The best evidence is to the effect that only preformed carbon dioxide 

 is given off by isolated muscles in the absence of oxygen. They 

 can go on contracting indeed, as previously stated, in an atmosphere 

 of hydrogen or nitrogen, and may seem to be producing carbon 

 dioxide, but the increased output appears to be due simply to an 

 accelerated decomposition of already existing carbonates, or perhaps 

 other combinations in which carbonic acid is loosely held, brought 

 about by lactic acid, which in the absence of oxygen, is not trans- 

 formed as it is under normal conditions, and accumulates in the 

 muscular substance, uniting with bases, and thus displacing 

 carbonic acid. 



Formation of Lactic Acid Reaction of Muscle. To litmus-paper 

 fresh muscle is amphicroic that is, it turns red litmus blue and blue 

 litmus red. This is due, partly at least, to the phosphates. Mono- 

 phosphate (tribasic phosphoric acid, H 3 PO 4 , in which one 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 fat \gued by prolonged 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 un- 

 necessary 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^mall excised muscles corresponds to a partial 

 asphyxia, there is a small increase in the lactic acid, but its pro- 

 duction 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 



49 



