60 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



point of the nutrition of the muscle. During muscular activity 

 the store of glycogen is used up, and if the activity is sufficiently 

 prolonged may be made to disappear entirely. Among the many 

 uncertain and contradictory statements regarding the chemical 

 changes in active muscle, this fact stands out in pleasant contrast 

 as one that is satisfactorily demonstrated. 



Phosphocarnic Acid (Nucleon). A peculiar substance con- 

 taining phosphorus was discovered by Siegfried in the muscle ex- 

 tracts.* This substance seems to resemble the proteids, but has a 

 complex and peculiar structure, as is shown by its split products 

 when hydolyzed by boiling with baryta water. Under these condi- 

 tions there are formed carbon dioxid, phosphoric acid, a carbohy- 

 drate body, succinic and lactic acids, and a crystallizable nitrogenous 

 acid body which is designated as carnic acid (C ]0 H 15 N 5 O 3 ). Siegfried 

 assumes that this latter substance is identical with one of the pep- 

 tones (antipeptone) formed during digestion, and conceives, there- 

 fore, that his phosphocarnic acid is a complex substance built 

 up from a peptone and a phosphorus-containing compound. Com- 

 pounds of simple proteids with phosphorus-containing bodies 

 (nucleic acids) are designated usually as nucleins; for this com- 

 pound of a peptone with a phosphorus-containing complex Sieg- 

 fried suggests the name of nucleon. By the addition of ferric 

 chlorid the nucleon is precipitated readily from muscle extracts 

 as an iron compound, carniferrin, and under this name has come 

 into the market as a presumably efficient therapeutic preparation 

 of iron. The discoverer of nucleon has attributed to it a very 

 great physiological importance, as a source of energy to the muscle, 

 and as an efficient means of transportation of iron, calcium, potas- 

 sium, and magnesium into the muscle substance, particularly in such 

 articles of diet as soups, bouillons, meat extracts, etc. It must be 

 stated, however, that there still remains some doubt as to the 

 chemical individuality of the nucleon or the nucleons, their existence 

 in normal muscle, and their physiological role. The substance, 

 whether a well-defined chemical individual or not, is most interest- 

 ing. Its properties are such as would aid in explaining the occur- 

 rence of some of the known products of the chemical changes during 

 contraction; but obviously further investigation is still needed 

 before such an application can be made with confidence. 



Lactic Acid (C 3 H 6 3 ). Lactic acid is found in varying amounts 

 in the extracts of muscle. The acid that is obtained is the so-called 

 ethidene lactic acid or a-hydroxypropionic acid (CH 3 CHOHCOOH), 

 and differs from the lactic acid as found in sour milk in that it ro- 

 tates the plane of polarized light to the right. The lactic acid in 



* Siegfried, "Zeitschrift f. physiol. Chemie," 21, 360, 1896; also 28, 524, 

 1899. 



