60 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



is consumed by the tissue during its activity, and it is assumed 

 that before it is thus consumed it is converted back into sugar by 

 the action of an amylolytic enzyme contained in the muscle. The 

 glycogen, therefore, itself represents a local deposit of carbohydrate 

 nutritive material, resembling in this respect the fat. The sugar 

 and the glycogen must be considered as one from the standpoint 

 of the nutrition of the muscle. During muscular activity the 

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

 longed it 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 containing phos- 

 phorus was discovered by Siegfried in the muscle extracts.* This substance 

 seems to resemble the proteins, but has a complex and peculiar structure, as 

 is shown by its split products when hydrolyzed by boiling with baryta water. 

 Under these conditions there are formed carbon dioxid, phosphoric acid,, 

 a carbohydrate body, succinic and lactic acids, and a crystallizable nitrogen- 

 ous acid body which is designated as carnic acid (C 10 H 15 N 5 O 3 ). Siegfried 

 assumes that this latter substance is identical with one of the peptones 

 (antipeptone) formed during digestion, and conceives, therefore, that his 

 phosphocarnic acid is a complex substance built up from a peptone and a 

 phosphorus-containing compound. Compounds of simple proteins with 

 phosphorus-containing bodies (nucleic acids) are designated usually as 

 nucleins ; for this compound of a peptone with a phosphorus-containing com- 

 plex Siegfried 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 t>he muscle, and as an efficient means of transportation of iron, 

 calcium, potassium, 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 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 interesting. Its properties are such as would aid in explaining 

 the occurrence 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 H H 6 O 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 -hydroxypropionic acid (CH 3 CHOHOOOH), 

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

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

 sour milk is produced by bacterial fermentation, and is inactive to- 

 polarized light, because it exists in racemic form ; that is, it con- 

 sists of equal amounts of the right-handed form which turns the 

 plane of polarization to the right and of the left-handed form 

 which turns it to the left. In the muscle the right-handed form 



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

 1899. 



