MUSCULAR TISSUE. 135 



to elastin, and its contents. The latter are mostly albu- 

 minous matters, alkaline and liquid during life, but be- 

 coming acid and more solid after death. This albuminous 

 liquid, which in many respects corresponds to the plasma 

 of the blood, is called muscle-plasma. It coagulates quickly 

 at the ordinary temperatures, and thus gives rise to the 

 rigor mortis of the muscles after death. The coagulated 

 mass is myosin: a mixture of a number of compounds. 

 The cause of the coagulation of the myosin in this case 

 is probably the formation of lactic acid, which accumulates 

 in the muscle after death. 



If fresh muscular tissue is treated with boiling water, 

 most of the albuminous substances are coagulated and 

 upon filtering remain with the fats in the insoluble residue. 

 The solution contains, besides inorganic matters, a class 

 of organic compounds, sometimes called, from the method 

 of obtaining them, the "extractives." They may be divided 

 into two groups: those which contain no nitrogen and 

 those of which nitrogen is a constituent. Among the non- 

 nitrogenous are lactic acid and its compounds; also gly- 

 cogen and its derivatives: dextrin, maltose, and glucose. 

 The principal ones of the nitrogenous extractives are 

 creatin and creatinin, small quantities of urea and uric 

 acid, and the nuclein bases, such as guanin, xanthin, and 

 hypoxanthin formerly called sarcin. Carnin, which is 

 similar in properties and composition to the nuclein bases, 

 is also found in the watery extract of muscle. 



Creatin: 



H 9 N HOCO 



I I 



I 



I I 



H 3 CN OH, 



