666 PHYSIOLOGICAL CHEMISTRY. 



says that it is converted first into an intermediate stage, and finally 

 into myogen fibrin. Myosin belongs to the globulins and myogen 

 resembles the albumins. The coagulation of these proteins appears 

 to take place spontaneously, as no enzyme has been satisfactorily 

 demonstrated. The process is probably not analogous to the clotting 

 of fibrinogen. 



Carbohydrates of muscle. There are present in muscle varying 

 amounts of dextrose and glycogen, which form probably the most 

 important source of energy for the work of the muscle. The dex- 

 trose is brought by the blood-stream, and any excess over the amount 

 needed for immediate use is converted into glycogen by the muscle, 

 and "is held in reserve in this form. When a muscle does work, i. e., 

 when it contracts, the glycogen is split again into dextrose, which is 

 then oxidized with a resulting liberation of energy. It is possible to 

 show that the carbon dioxide of the muscle is increased in amount, 

 and that there is also a formation of lactic acid. It is believed that 

 this lactic acid represents an incomplete oxidation of the sugar. In 

 the burning of dextrose by the muscle tissue, an internal secretion or 

 hormone produced by the pancreas is believed to play an important 

 part. 



Muscle extractives. The extractive bodies of the muscle are 

 important, and are both nitrogenous and non-nitrogenous. Among 

 the first, creatine, the xanthine bases, urea, and uric acid deserve men- 

 tion. Non-nitrogenous extractives always present are inosite, gly- 

 cogen, sugar, and lactic acid. 



Creatine (Meihyl-guanidine-acetic acid), NH = ^\TC/ip 2 TT \ p TT o 



=C 4 H 9 N 3 O 2 , occurs in muscles of vertebrates, in the brain, blood, 

 transudates, and the amniotic fluid. When pure, it forms colorless, 

 transparent, rhombic prisms. The crystals are soluble in 75 parts 

 of cold, much more soluble in hot water, slightly soluble in alcohol, 

 insoluble in ether. The solution is neutral to litmus, though creatine 

 is a weak base, combining with some of the acids to form crystal- 

 line salts. Creatine may be obtained by the action of cyanamide on 

 sarcosine (methyl-glycocoll). 



dride of creatine, and may be obtained by boiling creatine with acids, 

 when a molecule of water is split off. Vice versd, creatinine may 

 be converted into creatine. Creatinine is readily soluble in water 

 and alcohol, but nearly insoluble in ether ; it crystallizes in colorless 





