CHAP. IL] THE CONTRACTILE TISSUES. 69 



loses none of its translucency, the latter becomes less extensible, less 

 elastic, and less translucent. Corresponding to this marked differ- 

 ence, we find myosin formed in the rigid muscle, but we cannot 

 find it in the contracted muscle. 



The other chemical changes in muscle during a contraction 

 have not yet been clearly made out. Indeed our whole information 

 concerning the other chemical constituents of muscle is at present 

 imperfect. 



The bodies which we have called extractives are numerous and 

 varied. Among the nitrogenous crystalline extractives the most 

 important is kreatin, which occurs to the extent of about '2 to 

 3 p. c., is an invariable constituent of muscle, and is found elsewhere 

 only in nervous tissue, the kidney, and to a slight extent in the 

 blood. As we shall hereafter see, great interest is attached tot 

 this body inasmuch as it readily splits up into urea, and sarcosin, 

 and accordingly has been regarded as one at least of the antecedents ? 

 of urea, which body is conspicuous by its absence from muscular \ 

 tissue. The alkaline kreatinin into which kreatin is converted by 

 the action of acids, and which appears in the urine, is apparently 

 absent from muscle. The other nitrogenous crystalline bodies, 

 which need not detain us now, are karnin, hypoxanthin (or sarkin), 

 xanthin, inosinic acid, taurin and possibly uric acid 1 . 



Fats are present in considerable quantities both in the adipose 

 tissue between the bundles of fibres and also as constituents of the 

 muscular substance within the sarcolemma. 



The peculiar starch-like body, glycogen, of which we shall have 

 to speak more fully in a later part of this work, is especially 

 abundant in the muscles of the embryo at an early period, and 

 besides, is so continually met with in the muscles of the adult that 

 it may fairly be considered as a normal constituent of muscle to a 

 variable extent, possibly from '5 to 1 p. c. A dextrin-like body has 

 also been found, and at times glucose or an allied sugar. The 

 cardiac muscular tissue contains the peculiar sugar, inosit. 



The ashes of muscle, like those of the red corpuscles, are cha-J 

 racterised by the preponderance of potassium salts and of phos-j 

 phates ; these form in fact nearly 80 p. c. of the whole ash. 



The general composition of human muscle is shewn in the 

 following table of v. Bibra. 



Water 744'5 



Solids 



Myosin and other matters, elastic ele- 

 ments, &c., insoluble in water ... 155*4 



Soluble proteids 19'3 



Gelatin 207 



Extractives and Salts 37'1 



Fats 23-0 



255-5 

 1 See Appendix. 



