

ELEMENTARY PHYSIOLOGICAL CHEMISTRY 207 



If there be only two oxygen atoms present we obtain Xanthin, if only 

 one Hypoxanthin, and these two are the alloxuric bodies occurring in 

 muscle extracts. They result from the breakdown of nucleins in the 

 muscle. These nucleins contain alloxuric bodies in their molecule, 

 and the latter are excreted in the urine mainly as the more 

 highly oxidised body uric acid. A certain proportion is, however, 

 split up probably into urea, at any rate it is impossible to recover 

 the whole of hypoxanthin as uric acid in the urine when the former 

 is given with the food. 



The chief non-nitrogenous extractive is Lactic acid (C 3 H 6 3 ). It is 

 extracted from the creatin and purin-free liquor by shaking with ether. 

 After evaporating off the ether an acid syrup is obtained which is 

 neutralised by adding zinc carbonate, this leading to the formation of 

 zinc lactate. Chemically it consists of a-hydroxy-propionic acid, i.e. 

 propionic acid, CH 3 CH 2 - COOH, in which one of the H atoms of the 

 methyl radicle next the carboxyl group is replaced by hydroxyl (OH). 1 

 An acid of exactly the same constitutional formula is obtained by 

 the fermentation of lactose (see carbohydrates, p. 165), and under 

 special conditions of cane sugar. The acid obtained by the fermenta- 

 tion of milk sugar differs from sarco-lactic acid, however, in the fact 

 that it does not rotate the plane of polarised light in either direction, 

 whereas sarco-lactic acid rotates it to the right. 2 This different be- 

 haviour depends on the exact position of the various side groups in 

 relation to a central carbon atom (see Advanced Course). The test 

 for sarco-lactic acid is the same as for ordinary lactic acid, namely, 

 Uffelmann's reaction (see Milk, p. 188). 



EXPERIMENT III. Apply Uffelmann's test to the muscle extract. 



Another important nitrogen-free extractive is glycogen (C 6 H 10 5 )fl. 

 The relative amount of this is small (about '04 per cent.), but it varies 

 in different animals, and is much diminished after muscular activity. 

 Although the percentage is small the total amount contained in all the 

 muscles of the body has been found, in the case of the cat at least, to 

 be nearly the same as that contained in the liver. 



The less important extractives are : Urea, carnic acid (C 10 H 15 N 3 5 ) 

 (which is identical with antipeptone and exists in muscle combined with 

 phosphoric acid as phospho-carnic acid), dextrose (trace) inosinic acid 

 (also contains phosphorus, but its exact formula is unknown) and 

 lecithin. 



1 If it had been in the other methyl radicle that the substitution of OH for H 

 had occurred, the resulting body would have been jS-hydroxy-propionic acid. 



2 The lactic acid obtained by the growth of certain bacteria in a solution con- 

 taining cane sugar is levo-rotatory. 



