38 PHYSIOLOGY CHAP. 



with the enzyme which effects the coagulation or transformation 

 of myosinogen into myosin. Of the four coagulable proteins, two 

 (myosinogen and the paramyosinogen or musculin of Hammarsten) 

 form the clot, while the two found in the muscle serum (myo- 

 globulin and myoalbumiri) closely resemble or are identical with 

 those present in blood serum. 



Muscle serum holds the pigments to which the muscles owe 

 their colour in solution. The normal pigment of the red muscles 

 is due to haemoglobin, identical with that of the erythrocytes, as 

 was proved by Klihne (1865) from the spectrum of muscles 

 (diaphragm) that had been entirely freed from blood by prolonged 

 washing with saline. MacMunn (1884-87) afterwards investi- 

 gated the muscles of different classes of vertebrates and inverte- 

 brates, and found that they exhibited a variety of absorption 

 spectra, due in his opinion to a group of pigments which he 

 named myohaematin. According, however, to Hoppe-Seyler and 

 Levy (1889) myohaematin is only a decomposition product of the 

 haemoglobin of the muscle. That haemoglobin is an intrinsic 

 product of the muscle cells or fibres is shown by the fact that it 

 exists in the muscles of invertebrates which have no haemoglobin 

 in their circulating fluids. 



When the muscles of recently killed animals are treated with 

 boiling water the proteins coagulate, and the extract contains all 

 the soluble nitrogenous and non-nitrogenous organic substances of 

 the muscle. The first form a group of compounds which represent 

 different disintegration products of the proteins (creatine and 

 creatinine zanthine, hypozanthine, carnine, uric acid and urea 

 taurine and glycocoll). The second belong to the carbohydrate 

 group and its derivatives (glycogen, dextrin, glucose, maltose, 

 inosite, lactic acid, and lactates). 



Quantitatively speaking, creatine and glycogen (which we have 

 already discussed, Vol. II. pp. 391, 310) predominate among these 

 groups of substances in the muscle. 



Nothing definite is known at present about the physiological 

 importance of creatine and creatinine. They are certainly formed 

 by katabolic processes from the proteins in the muscle. In fact 

 they are more abundant in muscles which have been overworked 

 previous to the death of the animal (Monari, 1888) than in muscles 

 analysed after rest. Nawrocki and Sarokin, however, found that 

 the creatine-content is no larger in tetanised than in resting 

 muscle. Another striking fact was discovered by Demant (1879) 

 in Hoppe-Seyler's laboratory. In the muscles of pigeons starved 

 until they have consumed all the non-nitrogenous reserve materials 

 contained in the muscles, so that metabolism proceeds at the 

 expense of protein disintegration, the content of creatine and 

 creatinine amounts to three times that in normal pigeon muscle. 



Glycogen and its derivatives are the principal reserve material 



