168 AX AMERICAN TEXT- BOOK OF PHYSIOLOGY. 



Ergographic experiments on the human subject have proved that muscles 

 which have been fatigued by long-continued voluntary work recover much 

 more rapidly if sugar be eaten. Curiously enough, Waller and Miss Sowton 

 observed that the endurance of an isolated frog's nerve was increased, or at 

 least its capacity to develop strong currents of action was enhanced, if it was 

 put for a time in a <>.<> per cent, solution of sodium chloride containing dex- 

 trose. 



Lactic Acid. — This is formed in the muscle during work and during 

 coagulation. It has the form of para-lactic acid or sarco-lactic acid, though 

 it i.- doubtful whether it exists in a free state. It is a decomposition product 

 of the carbohydrates and perhaps of proteid or some complex muscle-sub- 

 stance of which proteid forms a part. It is only partly responsible for 

 acidity of the muscle which has been worked. The acidity may well he in 

 pari caused by acid potassium phosphate produced from alkaline phosphates 

 as a result of the formation of phosphoric acid from lecithin, nuelein, etc. 1 

 Rohmann 2 attributes the acidity of worked muscles to monopotassium phos- 

 phate, and the alkaline reaction of the resting muscle to dipotassium phos- 

 phate ami sodium bicarbonate. 



Inorganic Constituents of Muse/,. — Among the bases, potassium has the 

 greatest prominence, and sodium next: magnesium, calcium, and small amounts 

 of iron are also found. Of the acids, phosphoric is present in the largest quan- 

 tities. 



The quantity of a given substance present in a tissue is not an evidence 

 of its value, and the salts in the muscles, although present in comparatively 

 small quantities, are absolutely essential, not only to their functional activity, 

 but to their life. According to Loeb, 3 salts are not only present, as such, in 

 the muscle, but the ions Na, Ca, K, and Mg, are in combination with the 

 proteids, and these ion-proteid compounds are essential to its irritability (see 

 ,,. 58). 



Gases of Muscle. — Xo free oxygen can be extracted, but carbon dioxide 

 may be obtained, in part free and in part in combination. A little nitrogen 

 can also be extracted, but apparently it has no physiological significance. 

 Tin' amount of carbonic acid developed varies greatly with the condition of 

 the muscle ; for instance, it i- much increased by muscle work. Muscles 

 take up oxygen from the blood freely, especially when active, and when 

 removed from the body may absorb small amounts from the air. Moreover, 

 a certain amount of oxygen comes to the muscle from the food. More oxy- 

 gen is taken up by the muscle during rest than is liberated as carbon dioxide. 

 but during action the reverse is the case.' Oxygen is not retained as free 



1 Weyl imil Seither: Zeitschrift fur physiologische Cher/vie, vi. S. ~>~>7. 



: Rohmann : Pfluger'a Archiv, 1892, 1. S. - 1, and 1893, lv. 589. 



3 American Journal <■/' Physiology, 1900, vol. iii. p. 327. 



*Ludwig mid Sczelkow: Stizungsberichte der I:. Akad. Wien, 1862, Bd, xlv. Abthl. 1; and 

 Ludwig mid Schmidt : Sitzungsberichte '/<•>• mnih.-phys. Clasxe d. k. Sachs. GeseUschafi <!<>■ Wissen- 

 schaft, 1868, Bd. xx.; Regnault and Reisel : Annates d>- Ghimie et de Physique, 1849, 3tne s6r., 

 xxvi.; Pfliiger: Pfliiger's Archiv, 1>7"_\ vi. : and others. 



