76 TEXT-BOOK OF PHYSIOLOGY 



The Muscle Sound. If a stethoscope or a myophone with telephone 

 connections be placed on a muscle while in a condition of volitional tetanus 

 and at the same time kept in a certain degree of tension, there will be devel- 

 oped in the observer a sensation of sound or tone which is spoken of as a 

 muscle sound or tone. It is also readily heard in the masseter muscle when 

 the side of the face is placed on a receiving body such as a pillow, and the 

 masseter muscles made to contract volitionally. This tone is attributed to 

 a vibration or an alternate contraction or relaxation of the muscle or to an 

 intermittent rhythmic variation in tension, the result of the rate of stimula- 

 tion. This tone corresponds to a vibration frequency of from 18 to 20 per 

 second and is accepted as one of the proofs that the physiologic volitional 

 tetanus is not continuous but discontinuous in character. If a muscle is 

 tetanized with induced currents, the tone increases in pitch for a limited 

 time as the frequency of the current per second increases up to a certain 

 maximum, which for frogs is about 200 and for mammals about 1000. 



CHEMIC PHENOMENA 



The chemic changes which underlie the transformation of energy in the 

 living muscle even when in a state of relative rest are active and complex, 

 though but little is known as to their exact character. As shown by an 

 analysis of the blood flowing to and from the resting muscle, it has, while 

 flowing through the capillaries, lost oxygen and gained carbon dioxid. The 

 amount of oxygen absorbed by the muscle (9 per cent.) is greater than the 

 amount of carbon dioxid (6.7 per cent.) given off. Notwithstanding the 

 relation of the oxygen absorbed to the carbon dioxid produced, there is no 

 parallelism between these two processes, as the carbon dioxid will be given 

 off in the absence of free oxygen or in an atmosphere of nitrogen. 



If the muscle be stimulated through its related nerve all the chemic 

 changes are increased as shown both by an increased absorption of oxygen 

 and an increased production of carbon dioxid, though the ratio existing 

 between them differs considerably from that of the resting muscle. Thus, 

 according to Ludwig, an active muscle absorbs 12.26 per cent, of oxygen 

 and gives off 10.8 per cent, carbon dioxid. At the same time the muscle- 

 tissue changes from a neutral to an acid reaction, from the development of 

 sarcolactic acid and possibly phosphoric acid. The degree of the acidity 

 depends partly on the duration of the contraction periods. Chemic analysis 

 of a tetanized muscle shows that it contains less glycogen than a resting 

 muscle, and that it contains a larger amount of water. Coincident with 

 the muscle contraction, the blood-vessels become widely dilated, leading to a 

 large increase in the blood-supply and a rapid removal of the products of 

 decomposition. 



Rigor Mortis. A short time after death the muscles pass into a condi- 

 tion of extreme rigidity or contraction known as death stiffening or rigor 

 mortis, which lasts from one to five days. In this state they offer great 

 resistance to extension. At the same time their tonicity disappears, their 

 cohesion diminishes, and their irritability ceases. The time of the appear- 

 ance of this post-mortem rigidity varies from a quarter of an hour to seven 

 hours. Its onset and duration are influenced by the condition of the muscle 

 irritability at the time of death. When the irritability is impaired from any 



