TISSUES OF THE BODY. 297 



If, on the other hand, muscle be treated with a very dilute solution of 

 hydrochloric acid (1 : 1000), another modification of the albuminate group 

 is obtained, from the members of the latter contained in it, namely, 

 syntonin,. This body was formerly named " muscle fibrin," until Liebig 

 prove its difference from fibrin. It may be obtained, moreover, by a 

 similar process, from other albuminous matters, and is probably also 

 formed physiologically by the action of the acid gastric juice during 

 digestion. 



The quantity of syntonin varies very much in the muscles of different 

 animals (Liebig), and we are taught further, by the microscopic control of 

 the fibre engaged in solution, that we have here to deal, not with a simple, 

 but with a compound matter, consisting of three substances,- first, the 

 longitudinal cementing medium, which falls the first prey to the solvent 

 action of hydrochloric acid, and then the sarcous elements and transverse 

 cementing substance, which are probably not simultaneous in their 

 solution. Besides these, there remains over in the sarcolemma a slimy 

 granular residue with fatty molecules. 



Neither nucleus nor sarcolemma yield any of this syntonin. The first 

 affords no glutin (Scherer, Koelliker), but consists of a substance nearly 

 allied to elastin, but differing from it in its smaller power of resistance to 

 reagents ; the latter resists the action of dilute hydrochloric acid for days 

 in the most determined manner (fig. 277, 5, a, b), but gives way on the 

 other hand to strong alkaline solutions. 



Like all other tissues, muscle contains fat, but in most variable 

 quantity. A certain proportion of it may be set down to the cells of the 

 nerves and fat-cells of the fleshy mass, but a certain amount belongs to 

 the fibres themselves. 



By means of washing and expression, about G per cent, of constituents, 

 soluble in cold water, may be extracted from the dead muscles of the 

 mammalia. They are of very various nature and great physiological 

 interest. In the liquid so obtained, which is of reddish colour, opaque, 

 and of strongly acid reaction, we encounter, in the first place, a not incon- 

 siderable proportion of soluble albuminoids, amounting in the fresh tissue 

 to 2-3 per cent. 



We obtain in the first place, then, the red colouring matter of the 

 muscular fibres in solution, which is identical with that of the blood 

 (Kuhne), and with which the tissue is saturated during life. The tint of 

 striped muscular tissue is more intense than that of unstriped fibres, and 

 is, as a rule, only present, with any degree of markedness, among the 

 higher vertebrates, whilst the flesh of the lower members of this group 

 appears in general but slightly reddened, or even quite pale. 



Besides this, the juice of muscle contains, as shown by Liebig, a series 

 of important products of decomposition, which were known to earlier 

 investigators as " extractives." Among these there appear, in the first 

 place, several azotised substances. The first of these is kreatin (p. 44), 

 whose amount is usually small, existing, it is generally supposed, in largest 

 quantity in the heart. It varies also in different species of animals, 

 and is more abundant in lean than in fat bodies, and likewise after 

 muscular exertion. A hundred parts of fresh human muscle contain, 

 according to Schlossberger, O'OG of kreatin (in the horse. 0'07. according 

 to Liebig), while the heart yields 0'14 per cent. The next of the series 

 is Jcrealinin (p. 45) (nearly allied to the last), which appears to occur in 

 smaller quantity than the last. Its occurrence, however, appears doubtful 



