MUSCULAR TISSUE. 237 



in giving a reddish color with iodine and in being dextro-rotatory. 

 Glycogen may be prepared from muscle by extracting with boiling 

 water and then precipitating the glycogen from the aqueous solu- 

 tion by alcohol : dilute or concentrated potassium hydroxide may 

 also be used to extract the glycogen. Glycogen may be prepared 

 in the form of a white, tasteless, amorphous powder. It is com- 

 pletely precipitated from its solution by saturation with solid am- 

 monium sulphate, but is not precipitated by saturation with sodium 

 chloride. It may also be precipitated by alcohol, tannic acid or 

 ammoniacal basic lead acetate. It has the power of holding cupric 

 hydroxide in solution in alkaline fluids but cannot reduce it. It 

 may be hydrolyzed with the formation of dextrose by dilute min- 

 eral acids and is readily digested by amylolytic enzymes. 



Mendel and Leavenworth have recently drawn the conclusion, 

 from the examination of embryo pigs, that embryonic structures 

 do not contain exceptionally large amounts of glycogen. The dis- 

 tribution of the glycogen was not observed to differ from that in 

 the adult animal except that the liver of the embryo does not 

 assume its glycogen-storing function early. They further draw 

 the conclusion that the metabolic transformations of glycogen in 

 the embryo and the adult are entirely analogous. 



The lactic acid occurring in the muscular tissue of vertebrates 

 is paralactlc or sarcolactic acid, 



H OH 

 H-C-C-COOH. 



H 



The reaction of an inactive living muscle is alkaline, but upon the 

 death of the muscle, or after the continued activity of a living 

 muscle, the reaction becomes acid, due to the formation of lactic 

 acid. There is a difference of opinion regarding the origin of this 

 lactic acid. Some investigators claim it to arise from the carbo- 

 hydrates of the muscle, while others ascribe to it a protein origin. 



Among the nitrogenous extractives of muscle, those which are 

 of the most interest in this connection are creatine and the purine 

 bases, xanthine and hypoxanthine. Creatine is found in varying 

 amounts in the muscles of different species, the muscles of birds 

 having shown the largest amount. It has also been found in the 

 blood, the brain,. in transudates and in the thyroid gland. Creatine 



