236 PHYSIOLOGICAL CHEMISTRY. 



is somewhat doubtful. It is well established that para-myosino- 

 gen is a globulin since it responds to certain of the protein precipi- 

 tation tests and is insoluble in water. Myosinogen, on the con- 

 trary, is not a typical globulin since it is soluble in water. It has 

 been called a pseudo- globulin. Myosin possesses the globulin char- 

 acteristics. It is insoluble in water but soluble in the other pro- 

 tein solvents and is precipitated from its solution upon saturation 

 with sodium chloride. 



Very recently Mellanby has reported observations which he 

 claims indicate that there is only one protein in muscle and that 

 rigor mortis is due to the coagulation of this protein under the 

 combined influences of the salt present in the muscle and the lac- 

 tic acid developed upon the death of the muscle. He further states 

 that the disappearance of rigor is due to the fact that the lactic acid 

 which is continually formed brings this protein into solution. 



Under the name extractives we class a number of muscle con- 

 stituents which occur in traces in the tissue and may be extracted 

 by water, alcohol or ether. There are two classes of these extrac- 

 tives, the non-nitrogenous extractives and the nitrogenous extrac- 

 tives. Grouped under the non-nitrogenous bodies we have glyco- 

 gen, dextrin, sugars, lactic acid, inosite, C 6 H 6 (OH) 6 , and fat. In 

 the class of nitrogenous extractives we have creatine, creatinine, 

 xanthine, hypoxanthine, uric acid, urea, carnine, guanine, phospho- 

 carnic acid, inosinic acid, carnosine, taurine, carnitine, novaine, ig- 

 notine, neosine, oblitine, carnomuscarine and methylguanidine (see 

 formulas on page 240). Not all of these extractives are present in 

 the muscles of all species of animals. Other extractives besides 

 those enumerated above have been described and there are undoubt- 

 edly still others whose presence remains undetermined. A detailed 

 consideration would however be unprofitable in this place. 



Glycogen is an important constituent of muscle. The content 

 of this polysaccharide in muscle varies and is markedly decreased 

 by intense muscular activity. It is transformed into sugar 

 and used as fuel. The liver is the organ which stores the re- 

 serve supply of glycogen and transforms it into dextrose which is 

 passed into the blood stream and so carried to the working muscle 

 where it is synthesized into glycogen. The glycogen thus formed is 

 then changed into dextrose as the working muscle may need it. 



Glycogen is a polysaccharide and has the same percentage com- 

 position as starch and dextrin. It resembles starch in forming an 

 opalescent solution and resembles dextrin in being very soluble, 



