MUSCLE AND EXTRACTIVES. 339 



of water at the ordinary temperature its extraction from mus- 

 cle is easy. When the solution is boiled with dilute hydro- 

 chloric acid a molecule of water is split off and the anhydride 

 creatinine is left. This is a normal urinary constituent and 

 will be described later. When boiled with alkali solution, 

 especially baryta water, creatine undergoes a complete cleav- 

 age into urea and sarcosine, which relation is an interesting 

 one and has suggested the possible derivation of the urinary 

 urea. Creatine may be readily crystallized from water solu- 

 tion. It was formerly made for experiment directly fro>m 

 meat. It is best secured from certain crystalline residues oc- 

 curring as by-products in the manufacture of " beef extract," 

 referred to below. 



CARNINE. The amount of this in muscle is very small, 

 but it may be recognized in beef extract. It bears some rela- 

 tion in structure to hypoxanthine and has been given the for- 

 mula C 7 H 8 N 4 O 3 . 



THE XAXTHINE BODIES. These constitute a peculiar 

 group of great importance because of their relation to uric 

 acid. Traces of several of them have been recognized in the 

 muscular juices; in a later chapter the structure and proper- 

 ties of the substances will be discussed in connection with uric 

 acid. Traces of urea are also found in the muscles. 



The Nitrogen- Free Extractives. The muscular juices 

 hold dissolved a number of compounds which contain no ni- 

 trogen, some of which are very important. The chief of 

 these are glycogen, inosite, glucose and lactic acid. 



GLYCOGEN. The chemical relations of glycogen have been 

 discussed already in earlier chapters. The glycogen as found 

 in the muscles comes from the liver, being transported there 

 by the blood, and in part is probably formed in the muscles 

 by the same kind of an enzymic action which leads to its syn- 

 thesis in the liver. The liver is capable of storing up a large 

 weight of the reserve substance in a small space. The amount 

 stored in an equal weight of muscle is small, but taking the 

 muscles of the body as a whole the glycogen content is con- 

 siderable, reaching a hundred grams or more. 



