376 THE MUSCLE-TISSUE. 



The amount of lactic acid that may be isolated from dead muscles 

 while still rigid varies between 0.1 and 1.0 per cent., and it is note- 

 worthy that for definite groups of muscles this amount is constant, 

 no matter whether the formation of the acid is allowed to proceed 

 rapidly or slowly. This, however, holds good only for correspond- 

 ing muscles, and is different in different groups. In rabbits larger 

 amounts can thus always be obtained from the muscles of the trunk 

 than from those of the extremities. 



To the general rule that the acidity of corresponding muscles is 

 always the same, there is one exception, viz., the heart, which is the 

 only muscle of the body, moreover, that normally presents an acid 

 reaction. Larger amounts of lactic acid are here always found in 

 the left than in the right side. 



As regards the origin of lactic acid in muscle-tissue, it was long 

 thought that the glycogen probably represented its principal source. 

 There are a number of facts indeed which favor such an assumption. 

 I have pointed out already that after death the glycogen gradu- 

 ally disappears, and we have just seen that lactic acid is then found. 

 Glycogen is similarly decomposed during muscular activity in the 

 living animal, where lactic acid is also constantly produced, and, as 

 I have shown, the same also occurs in the muscle while at rest. 

 Then again there is evidence to show that during the decomposition 

 of glucose in the muscle- tissue lactic acid may be one of the result- 

 ing products. But, on the other hand, observations exist which go 

 to show that the amount of lactic acid that is produced during rigor 

 mortis bears no relation to the amount of glycogen which was 

 present at the time, and it has further been noted that lactic acid is 

 still formed in muscles from which all glycogen has previously been 

 removed by starvation. The conclusion hence suggests itself that 

 while a certain amount of lactic acid may be derived from glycogen, 

 this does not represent its only source, and we must admit that to 

 some extent the albumins of muscle-tissue also contribute toward its 

 formation. There is a tendency among physiological chemists at 

 the present time to regard this source indeed as the most important. 

 We have seen that Siegfried's phospho-carnic acid gives rise 

 to the formation of lactic acid on hydrolytic decomposition, and it 

 is thus possible that this substance may be its immediate antecedent. 

 Further researches, however, are necessary before the formation of 

 lactic acid from the muscle-albumins can be satisfactorily explained. 

 Whether or not enzymotic influences are here at work we do not 

 know. Salkowski denies this possibility on the basis that lactic acid 

 is not found among the products of autodigestion when perfectly 

 fresh muscle- tissue is allowed to stand in contact with chloroform- 

 water, as the chloroform, according to this observer, does not pre- 

 vent the action of enzymes. If this property holds for all ferments, 

 the conclusion would also follow that the formation of lactic acid 

 can neither be referable to the action of living protoplasm, as the 

 chloroform represents a strong protoplasmatic poison. We have 

 seen, as a matter of fact, that muscle-plasma also becomes acid after 



