298 MANUAL OF HISTOLOGY. 



from Neubaur's investigations. Then we find hypoxanfhin (p. 43). 

 Strecker states the amount of the last of these to be only 0'022 per 

 cent, in the fresh flesh of oxen. In addition to these, a fourth substance, 

 xanthin (p. 43) is supposed by Scherer and Staedeler to exist in the flesh 

 of mammals. A new substance, discovered by Weidel in Liebig's extract, 

 may also be mentioned here, to which the name of carnin has been given. 

 Urea is not usually present in human muscle ; tyrosin and leucin are also 

 absent (2). The muscles of embryonic pigs of two inches long, however, 

 contain, besides kreatin, a moderate amount of leucin. 



In muscular tissue also there is a peculiar species of spurious sugar, 

 which has been named inosite (p. 33), and which has up to the present 

 only been met with in the substance of the heart. According to Valen- 

 tiner, it appears to be a normal constituent of the muscles of drunkards (3). 

 Staedeler met with it also in the muscles of dogs. Meissner has likewise 

 demonstrated the presence of a kind of sugar, " muscle sugar," peculiar to 

 muscle, in the flesh of the five classes of vertebrata, although as yet no one 

 has succeeded in obtaining it in a pure state. It is a matter of some 

 interest, further, that the embryonic muscle fibre, as well as the contractile 

 fibre-cell, both contain glycogen (Rouget, Bernard, and Kuhne) ; but it 

 appears also to be regularly present at a later period (0. Nasse). 



In that the muscles of phytophagous mammals contain dextrin, the 

 occurrence of this muscle sugar is easily explained. 



The series of organic acids is no less considerable. In the first place, we 

 have G'6-0'7 per cent, vfparalac&ic acid (p. 34) the source, apparently, 

 of the acid reaction of dead muscle. It was formerly supposed with 

 Licbig that it was a component of every living muscle also, but Du Bois- 

 Reymond showed later that the plasma of quiescent or moderately active 

 muscle has a neutral or weakly alkaline reaction, and only becomes acid 

 when the structure has been called on for immoderate exertion. On the 

 other hand, after the death of the muscle, which is ushered in by rigor 

 mortis, the fluid of its parenchyma becomes rapidly acid by virtue of the 

 presence of free lactic acid. As to the particular constituent of the 

 muscle from which this acid has its origin, we are at present unable to 

 answer anything with certainty. 



Besides this, we meet with inosinic acid (p. 36), according to Liebig, 

 about which but little is known, and which appears also in very small 

 quantity. Schlossberger, however, was unable to discover it in human 

 flesh. Further, muscle juice contains of the volatile fatty acid group 

 bvtyric, acetic, and formic acids. Uric acid was only once met with by 

 Liebig. 



Finally, the mineral constituents of muscle (of the tissue as well as con- 

 tained fluid) are very peculiar. The same compounds as those occurring 

 in the plasma of blood are certainly met with, but in completely different 

 proportions. While in the latter the combinations of soda preponderate, 

 muscle tissue shows the greatest poverty in soda, and an excess of potash. 

 In contrast also to the plasma of blood, the phosphatic salts exceed in 

 muscle the combinations of chlorine by a large amount, the greater part 

 of the phosphoric acid being united with potash, and the proportion 

 of chloride of sodium appearing but very inconsiderable. In conclusion, 

 among the combinations of phosphoric acid with earths, we find the 

 magnesian phosphate exceeding in amount the corresponding salt of 

 calcium. Iron is also contained in flesh in a small quantity. The absence 

 of sulphates is rather remarkable. 



