CAUSES AND PHENOMENA OF MOTION. 21 



I. EEST. 



Physical Condition. During rest or inactivity a muscle has a slight 

 but very perfect elasticity; it admits of being considerably stretched; but 

 returns readily and completely to its normal length. In the living body the 

 muscles are always stretched somewhat beyond their natural length, they 

 are always in a condition of slight tension; an arrangement which enables 

 the whole force of the contraction to be utilized in approximating the 

 points of attachment. It is obvious that if the muscles were lax, the first 

 part of the contraction till the muscle became tight would be wasted. 



There is no doubt that even in a condition of rest oxygen is being 

 abstracted from the blood and carbonic acid given out by a muscle; for the 

 blood becomes venous in the transit, and since the muscles form by far 

 the largest element in the composition of the body, chemical changes 

 must be constantly going on in them as in other tissues and organs, 

 although not necessarily accompanied by contraction. When cut out of 

 the body such muscles retain their contractility longer in an atmosphere 

 of oxygen than in an atmosphere of hydrogen or carbonic acid, and during 

 life, an amount of oxygen is no doubt necessary to the manifestation of 

 energy as well as for the metabolism going on in the resting condition. 



Chemical composition. The reaction of living muscle is neutral or 

 slightly alkaline. The substance or muscle plasma which forms the con- 

 tractile principal element in its composition undergoes coagulation when 

 the muscle is removed from the body, and the process may be observed 

 if the coagulation be delayed by cold. If the muscles of a frog be frozen, 

 minced whilst in that condition, and reduced to a pulp by being rubbed 

 up with a 1 per cent, solution of sodium chloride, the temperature of 

 which must be very low, on filtration in the cold, a colorless, somewhat 

 turbid filtrate separates with difficulty, which is muscle plasma. This 

 fluid at the ordinary temperature of the air undergoes a coagulation or 

 clotting, by which it is separated, as in the case of blood, into muscle- 

 serum and muscle-clot. The latter, however, is not made up of fibrin but of 

 myosin, which is a globulin (p. 328, Vol. II.). Myosin may also be obtained 

 from dead muscle by subjecting it, after all the blood, fat, fibrous tissue, 

 and substances soluble in water, have been removed, to a ten per cent, 

 solution of sodium chloride, filtering and allowing the- filtrate to drop into 

 a large quantity of water; myosin separating out as a white flocculent 

 precipitate. Obtained in either way, viz., from living or dead muscle, 

 myosin is soluble in dilute saline solutions, and the solution undergoes 

 coagulation at a lower temperature than serum-albumin or paraglobulin, 

 viz., at 131 140 F. (55 60 C.). It is coagulated also by alcohol. 

 It is dissolved and converted into acid-albumin by dilute acid, such as 

 hydrochloric. 



