446 MANUAL OF PHYSIOLOGY. 



changed into syntonin or acid albumin, and forms the prepon- 

 derant albuminous 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) Haemo- 

 globin. (3) Grape sugar, muscle sugar, or inosit, and glycogen. 

 (4) Sarcolactic 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 

 extent, or, in other words, the elastic force of muscle increases 

 with its extension. 



If a tracing be drawn showing the extending effect of a series 

 of equal weights attached to a fresh muscle, it will be found that 

 a great difference exists between it and a similar record drawn 

 by inorganic bodies or an elastic band of rubber. 



When a weight is applied to a muscle, it does not immediately 



