398 PROCESSES INFERRED FROM DIRECT OBSERVATION 



There has been some discussion of the question whether the lactic 

 acid of muscular tissues actually arises from the partial oxidation of 

 carbohydrates or whether it may not, on the contrary arise from 

 Proteins, as, for example, by the deaminization of the Alanine radical of 

 proteins: 



CH 3 CH 3 



I I 



CHNH 2 + H 2 O = CHOH + NH 3 

 I 

 COOH COOH 



Alanine. Lactic acid. 



While such an origin of sarcolactic acid must be admitted to be 

 possible, yet it is more probable that the major part of the lactic acid 

 produced by the muscular and other tissues of the body, arises from 

 a carbohydrate source. Thus Mandel and Lusk have shown that in 

 Phosphorus-poisoning there is a great increase in the lactic-acid output 

 in the urine. If, however, the body has previously been drained of its 

 carbohydrate reserve by inducing Glycosuria through the administra- 

 tion of Phloridzin, then phosphorus-poisoning results in no hyper- 

 production of lactic acid. 



The lactic acid in excised muscles of the frog rapidly diminishes on 

 standing. This is due to its oxidation by the muscle-tissues. Now the 

 oxidation of lactic acid is evidently a more difficult step to accomplish 

 than its production from glucose or glycogen, for, if the oxygen supplied 

 to the muscles be interfered with by asphyxia, by inhalation of air poor 

 in pxygen, or by poisoning with Carbon Monoxide, the lactic-acid con- 

 tent of the tissues and of the blood and urine is enormously increased. 



One of the characteristics of extreme muscular Fatigue is the stiffen- 

 ing and inextensibility of the muscles which ensues. After death the 

 Rigor Mortis or postmortem stiffening of the muscles occurs with 

 extreme rapidity if the animal has immediately prior to death been 

 engaged in extreme and prolonged muscular exertion. The stiffening 

 and increased opacity of the muscles which occurs after extreme fatigue 

 or death is due to the coagulation of certain proteins which the muscle- 

 fluids contain, the semifluid Muscle-plasma being converted into a 

 jelly. 



It was found by Halliburton that if muscles be frozen and minced 

 and then subjected to pressure at a temperature slightly above freezing, 

 an opalescent fluid is obtained which clots spontaneously upon warming 

 to a little above bodily temperatures, or upon standing for some time at 

 room-temperatures. According to von Fiirth the gelatinization of 

 this fluid is due to changes which occur in two proteins, the one a globu- 

 lin, Myosin and the other an albumin, Myogen. The myogen fraction 

 is much the more abundant of the two. Upon heating or acidification 

 these soluble proteins are transformed, respectively, into Myosin 

 Fibrin and Myogen Fibrin. The process is not reversible; the jelly 

 cannot be liquified by cooling or by neutralization. It is believed that 

 the partial gelatinization of these proteins which constitutes rigor in 



