CHAPTER II. 



CHEMISTRY OF MUSCLE. THE CHEMICAL CHANGES OF 

 CONTRACTION AND RIGOR. THEORIES OF MUSCU- 

 LAR CONTRACTION. EXERCISE AND STRAIN. 



Muscle Plasma. — The beginning of our present knowledge of 

 the chemical composition of muscle is found in some interesting ex- 

 periments made by Kiihne upon frog's muscle. Kiihne froze the 

 living muscle to a hard mass, cut it into fine shavings with cold 

 knives, and ground the pieces thoroughly in a cold mortar. The 

 fine muscle snow thus obtained was put under high pressure and 

 a liquid expressed which was assumed to represent the fluid living 

 substance in the normal fiber. This muscle plasma clotted on stand- 

 ing, much as blood does, the muscle clot shrinking and squeezing 

 out a muscle serum. Similar experiments have since been per- 

 formed by Halliburton* on mammalian muscle. 



Composition of the Muscle Plasma. — Using the term muscle 

 plasma to designate the entire contents of the muscle fiber within 

 the sarcolemma, it is obvious that this material should contain all 

 the constituents that properly belong to the muscle, in contradis- 

 tinction to the substances found in the connective tissue binding 

 the muscle fibers together. 



The constituents in addition to water that are known to occur 

 in muscle are very numerous indeed, and difficult to classify. They 

 may be grouped under the following heads: (1) Proteins. (2) Car- 

 bohydrates and fats. (3) Nitrogenous extractives (creatin, urea, 

 etc.). (4) Non-nitrogenous extractives (lactic acid, inosite, etc.). 

 (5) Pigments. (6) Ferments. (7) Inorganic salts. Very little 

 that is positive can be stated regarding the physiological role 

 of most of these constituents, the interest that attaches to them 

 at present being largely on the chemical side. 



The Muscle Proteins, f — The proteins of the muscle have been 

 investigated by a number of observers, but unfortunately the 

 terminology employed has not been uniform, and the facts so far 



* Halliburton, "Journal of Physiology," 8, 133, 1888. 



t Von Furth, "Archiv f. exper. Path. u. Pharmakol.," 36, 231, 1895, and 

 "Handbuch der Biochemie," 1909, vol. 2, p. 244; Halliburton, "Journal of 

 Physiology," 8, 133, 1888; Stewart and SoUman, ibid., 24, 427, 1899. 



