MUSCULAR TISSUE 



363 



the stomach of the frog and the striated muscle from the same animal 

 was very recently reported by Meigs and Ryan. 1 Their data indicate 

 "that smooth muscle contains somewhat less potassium and phos- 

 phorus and somewhat more sodium and chlorine than the striated 

 muscle of the same animal, but that the differences in these respects 

 between the two tissues are not by any means so marked as has some- 

 times been supposed." Their average figures for each type of muscle 

 follow : 



The preparation from which the above data for smooth muscle 

 were obtained were shown by histological examination to consist in 

 large part of smooth muscle fibers. 



Muscular tissue is said to contain a reddish pigment called myo- 

 hematin, which is a derivative of hemoglobin. 



The so-called "fatigue substances" of muscle are carbon dioxide, 

 paralactic acid, and potassium dihydrogen phosphate. 



The ordinary commercial "meat extract" is composed principally 

 of the water-soluble constituents of muscle and contains practically 

 nothing of nutritive value. The protein material to which meat owes 

 its value as an article of diet is ordinarily practically all removed in 

 the preparation of the extract. Occasionally some preparations are 

 found to contain proteose, which is formed from the meat proteins in 

 the process of preparation. 



Lusk 2 has shown that Liebig's extract is without influence upon the 

 metabolism (energy) in spite of the glandular activity it is known to 

 induce. 



The structural formulas of some of the nitrogenous extractives of 

 muscle are as follows: 



NH 2 

 HN=C 



HN 



I 

 HN=C 



CO 



i 



N(CH 3 ).CH 2 .COOH. 



CREATINE, CiHtNsOj. 



M ethyl-guanidine acetic acid. 



1 Meigs and Ryan: Journal of Biological Chemistry, n, 401, 1912 

 'Lusk: Jour. Biol. Chem., 13, 155, 1912. 



N(CH 3 ).CH 2 



CREATININE, CiHT 

 Creatine anhydride. 



