THE TISSUES 43 



3. Fat is present in small quantities. 



4. Inosite, formerly called muscle sugar, is present in small 

 amounts. It is not a sugar, but a benzene compound. 



5. Sarcolactic Acid. Hydroxy-propionic acid 



H OH 

 H C C C H 



This isomer of ordinary lactic acid is increased in muscle 

 during activity and during death stiffening. 



6. Extractives. If dried muscle is treated with alcohol a 

 series of bodies containing nitrogen may be extracted. The 

 chief of these is Creatin, or methyl-guanidin-acetic acid. 

 Guanidin C.NH(NH 2 ) 2 is a near ally of urea CO(NH 2 ) 2 

 being formed by replacing the with NH. 



Methyl-guanidin is produced by replacing an H in gua- 

 nidin by CH 3 



NH CH, 



I! I ' 

 H 2 N C N H 



If this is linked to acetic acid 



H N 



H 2 N C N- 

 Methyl-guanidin 



H 



-LL 



OH 



acetic acid 



is produced. 



7. The Colour of Muscle varies considerably, some muscles 

 being very pale, almost white in colour e.g. the breast 

 muscles of the fowl ; others again being distinctly red, even 

 after all the blood has been removed. This red colour is, in 

 some cases, due to the presence of the pigment of blood, 

 hcemoglobin, but in certain muscles it is due to a peculiar 

 set of pigments, Myohaematins, giving different reactions from 

 the blood pigment. 



