298 ELEMENTARY PHYSIOLOGY less. 



After the lapse of a certain time the coagulated matter 

 liquefies, and the muscles pass into a loose and flabby con- 

 dition, which marks the commencement of putrefaction. 



If a muscle taken perfectly fresh from the body be 

 cooled down with ice in order to keep it from undergoing 

 change (just as was previously done with blood, p. 107) 

 and subjected to considerable pressure it yields a fluid 

 called muscle plasma. This remains fluid so long as 

 it is kept ade(iualely cooled, but dots spontaneously at 

 ordinary temjjeratures, and may be made to clot when cold 

 by the addition of small quantities of acid. This clotting 

 results in the formation of a semi-solid gelatinous 

 substance, called myosin, and a small amount of fluid, 

 or muscle serum. Myosin is a protein and belongs to 

 the same class of proteins as do the fibrinof^en and para- 

 globulin of blood, namely the globulins. 



Besides myosin, muscle contains other varieties of 

 protein material about which we at present know little ; 

 a variable quantity of fat ; certain inorganic saline 

 matters, phosphates and potash being, as is the case in 

 the red blood-corpuscles, in excess ; and a large number 

 of substiinces existing in small quantities, and often 

 clas.sed together as "extractives." Some of these 

 extractives contain nitrogen ; the most abundant of this 

 class is creatine. It has been inferred that creatine is 

 converted into urea, the most abundant waste product of 

 the body, but of this there is no proof. 



The otiier class of extractives contains bodies free from 

 nitrogen, perhaps the most important of which are 

 sarcolactic acid and glycogen. 



Most muscles are of a deep, red colour ; this is due in 

 part to the blood remaining in tlieir vessels ; but only in 

 part, for each fibre (into which no capillary enters) has 

 a reddish colour of its own, like a blood-corpu.scle but 

 fainter. And this colour is probably due to tlie fibre 

 possessing a small quantity of tliat same haemoglobin ia 

 which the blood-corpuscles are so rich. 



