PHYSIOLOGICAL CHEMISTRY 355 



apply the thiophene test. It will be found that the muscles of the tetanized 

 limb give a positive reaction; those of the non-tetanised do not. 

 The tetanised limb having no circulation was poorly supplied with 

 oxygen. If it had been kept in an atmosphere of oxygen, the lactic 

 acid formed on tetanisation would have rapidly disappeared, so that 

 fatigue would have developed more slowly, and would have dis- 

 appeared rapidly on keeping the limb at rest in the oxygen of the 

 ordinary room temperature (Fletcher and Hopkins). The explanation 

 is that with plenty of oxygen any lactic acid formed is rapidly 

 destroyed with the evolution of carbon dioxide. With an intact circu- 

 lation lactic acid is certainly formed in the muscles with even short 

 periods of violent exercise, since Ryffel has shown that under these 

 conditions lactic acid is present in increased amount in the urine. 

 This being the case it is probable that the formation of this acid is one 

 of the causes leading to the hyperpnoea which attends hard muscular 

 exercise (see page 459). 



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

 The relative amount of this is small (0*5 to 1 %), 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 exists in muscle combined with phosphoric acid as phospho- 

 carnic acid), dextrose (trace), inosite (hexahydroxybenzene), and 

 lecithin. 



Carnic Acid. If a weak solution of ferric chloride be added to a muscle 

 extract (from which the proteins have been removed by boiling and the phosphates 

 by the addition of calcium chloride and ammonia) a brown precipitate is 

 obtained. This is called Carniferrin, and consists of the iron salt of phospho- 

 carnic acid. If, further, the phosphoric acid and iron be split off from this we 

 obtain carnic acid, and this, curiously enough, has the same formula as, and gives 

 nearly all the reactions of, one of the varieties of peptone known as antipeptone. 



Inorganic Salts. These consist of salts of the alkalies and alkaline 

 earths. The chief acid radicle present is phosphoric acid, and this exists 

 in several states (a) Inorganic phosphates, (b) phosphorus of lecithin, 

 (c) phosphorus of nuclein, (d) phosphorus of phospho-carnic acid, (e) 

 besides these the watery extract contains another phosphorus-con- 

 taining organic compound of unknown composition. 



Phosphorus, therefore, seems to be a very important constituent of 

 muscle, and its form of combination changes after muscular work, the 

 organically combined phosphorus being split off as inorganic phosphates 



