62 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



the development of special enzymes. A proteolytic enzyme capable 

 of digesting proteids has been described by Briicke and others; 

 an amylolytic enzyme capable of converting the glycogen to sugar 

 by Nasse; a glycolytic enzyme capable of destroying the sugars 

 by Brunton, Cohnheim, and others; a lipase capable of splitting 

 the fats by Kastle and Loevenhart; and, finally, a coagulating 

 enzyme responsible for the coagulation of the muscle plasma after 

 death by Halliburton. 



The Inorganic Constituents. Muscle tissue contains a number 

 of salts, chiefly in the form of the chlorids, sulphates, and phos- 

 phates of sodium, potassium, calcium, magnesium, and iron. As 

 in other tissues, the potassium salts predominate in the tissue itself. 

 These inorganic constituents are most important to the normal 

 activity of the muscle, and, indeed, in two ways: first, in that they 

 maintain a normal osmotic pressure within the substance of the 

 fibers and thus control the exchange of water with the sur- 

 rounding lymph and blood; second, in that they are necessary 

 to the normal structure and irritability of the living muscular 

 tissue. Serious variations in the relative amounts of these salts 

 cause marked changes in the properties of the tissues, as is ex- 

 plained in the section on nutrition, in which the general nutritive 

 importance of the salts is discussed, and also in connection with 

 the cause of the rhythmical activity of the heart. 



Chemical Changes in the Muscle during Contraction and 

 Rigor. Perhaps the most significant change in the muscle during 

 contraction is the production of carbon dioxid. After increased 

 muscular activity it may be shown that an animal gives off a 

 larger amount of carbon dioxid in its expired air. In such cases 

 the carbon dioxid produced in the muscles is given off to the 

 blood, carried to the lungs, and then exhaled in the expired air. 

 Pettenkofer and Voit, for instance, found that during a day in 

 which much muscular work was done a man expired nearly twice 

 as much C0 2 as during a resting day. The same fact can be 

 shown directly upon an isolated muscle of a frog made to con- 

 tract by electrical stimulation. The carbon dioxid in this case 

 diffuses out of the muscle in part to the surrounding air, and 

 in part remains in solution, or in chemical combination as car- 

 bonates, in the liquids of the tissue. It has been shown by 

 Hermann* and others that a muscle that has been tetanized gives 

 off more carbon dioxid than a resting muscle when their contained 

 gases are extracted by a gas pump. This C0 2 arises from the 

 oxidation of the carbon of some of the constituents of the muscle, 

 and its existence is an indication that in their final products the 



* Hermann, " Untersuchungen uber den Stoffwechsel der Muskeln, etc.," 

 Berlin, 1867. 



