CHEMISTEY OF MUSCLE. 443 



the thick juice is really the contractile substance, and it has been 

 called muscle plasma. 



The coagulation of muscle plasma reminds us in many ways of 

 the clotting of the blood plasma, but the muscle clot, or myosiu, 

 which is gelatinous and not in threads like fibrin, is a globulin, and 

 is soluble in ten per cent, solution of salt. It is readily changed 

 into syntonin or acid albumin, and forms the preponderant albu- 

 minous substance of muscle. 



The serum of dead muscle has a distinctly acid reaction, and 

 contains three distinct albuminous bodies coagulating at different 

 temperatures, one of which is serum-albumin,and another a derived 

 albumin, potassium-albumin. The serum of muscle also contains : 

 (1.) Kreatin, kreatinin, xanthin, etc. (2.) Haemoglobin. (3.) 

 Grape sugar, muscle sugar, or inosit, and glycogen. (4.) Sarco- 

 latic acid made from the inosit by fermentation. (5.) Carbonic 

 acid. (6.) Potassium salts ; and (7.) 75 per cent, of water. Traces 

 of pepsin and other ferments have also been found. 



Chemical change. In the state of rest a certain amount of 

 chemical change constantly goes on, by which oxygen is taken 

 from the haemoglobin of the blood in the capillaries, and carbonic 

 acid is given up to the blood. These changes seem necessary for 

 the nutrition, and therefore the preservation of the life and active 

 powers of the tissue, because if a muscle after removal be placed 

 in an atmosphere free from oxygen, it soon loses its chief vital 

 character, viz., its irritability. 



Elasticity. Striated muscle is easily stretched, and, if the ex- 

 tension be not carried too far, recovers very completely its original 

 length. We say then that the elasticity of muscle is small or 

 weak, but very perfect. When the muscle is stretched to a given 

 extent by a weight say of one gramme if another gramme be 

 then added it will not stretch the muscle so much as the first 

 did ; and so on if repeated gramme weights be added one after 

 the other, each succeeding gramme will cause less extension of 

 the muscle than the previous one ; so that the more a muscle is 

 stretched the more force is required to stretch it to the given ex- 

 tent, or, in other words, the elastic force of muscle increases with 

 its extension. 



