528 Creatin Content in Muscle [April-July 



a temporary increase in the quantity of creatin present in muscle 

 when there is an accumulation of creatin in the blood. 



The significance of muscle creatin is still obscure. That it is 

 not an essential constituent of protoplasm is evident, for inverte- 

 brates are entirely free from even traces of creatin. Invertebrate 

 muscle contains, however, other extractives that are not characteris- 

 tic of the vertebrate muscle, such as betain. The presence of creatin 

 in vertebrate muscle may be an indication of a type of metabolism 

 characteristic of vertebrates.^ That creatin, or its analogue in 

 invertebrates, is an essential structural dement has been inferred, by 

 some, from its constant presence in muscle. This fact would not, 

 however, preclude the possibility of its being a waste product (in 

 an intermediate stage of catabolism) that has been carried as far 

 along the line of chemical decomposition as the muscle cells are 

 capable of Converting it, other cells dehydrating it into Creatinin. 

 Improved methods of analysis have recently shown, however, that 

 Creatinin exists in minute amounts in muscle tissue, which fact tends 

 to assign to muscle the property of Converting creatin into Creatinin. 

 Myers and Fine have observed the conversion of creatin into Cre- 

 atinin in autolyzing muscle, or the reverse, depending upon the rela- 

 tive proportions of the two substances. 



Assuming that the creatin in living muscle is different from that 

 in post-mortem muscle, and amplifying the conception of Urano, in 

 which creatin is considered to be combined and held in muscle in 

 some non-dialyzable form, Folin"^ has suggested that " living muscles 

 contain virtually no creatin, and that the creatin found on analysis 

 is a post-mortem product originally constituting a part of the liv- 

 ing protoplasm." It is from this complex, Polin further concludes, 

 that Creatinin originates in normal metabolism but in unusual condi- 

 tions there is "an abnormal breakdown into creatin." If this com- 

 plex is the source of the Creatinin of the urine, such a conception 

 harmonizes with that relating to the diminished Creatinin excretion 

 in the urine coincident with a decreased quantity of muscular tissue. 

 For, as the cell mass becomes less (there is probably never a com- 



^ Wilson : Jour. Biol. Chem., 1914, xvii, p. 385. 



^ Myers and Fine : Jour. Biol. Chem., 1914, xvii, p. 65 ; Folin : Ibid., p. 475 ; 

 Shaff er : Ibid., xviii, p. 525. 



^ Folin : Jour. Biol. Chem., 1914, xvii, p. 493. 



