422 MOVEMENTS 



coagulates at 146 Fahr. (63 C.). This is called myoglobulin. (4) An 

 albumin, analogous to serum-albumin, called myo-albumin. 



Combined with the organic constituents of the muscular substance 

 are mineral salts in great variety, which cannot be separated without 

 incineration. Certain excrementitious matters have also been found in 

 the muscles ; and probably nearly all those eliminated by the kidneys 

 exist here, although they are taken up by the blood as fast as they are 

 produced and consequently are detected with difficulty. The muscles 

 also contain inosite, inosic acid, lactic acid, and certain volatile acids of 

 fatty origin. During life the muscular liquid is slightly alkaline, but it 

 becomes acid soon after death. The muscle itself, during contraction, 

 has an acid reaction. The muscular juice is alkaline or neutral after 

 moderate exercise as well as during repose ; but when a muscle is made 

 to undergo excessive exercise, the lactic and other acids exist in greater 

 quantity and the reaction becomes acid. 



PHYSIOLOGICAL PROPERTIES OF THE MUSCLES 



The important general properties of the striated muscles are the 

 following: I. elasticity; 2. tonicity; 3. sensibility of a peculiar kind ; 

 4. contractility and excitability. These are all necessary to the physio- 

 logical action of the muscles. Their elasticity is brought into play in 

 opposing muscles or sets of muscles ; one set acting to move a part and 

 to extend the antagonistic muscles, which, by virtue of their elasticity, 

 retract when the extending force is removed. Their tonicity is an in- 

 sensible and a more or less constant contraction, by which the action of 

 opposing muscles is balanced when both are in the condition of what is 

 called repose. Their sensibility is peculiar and is expressed chiefly in 

 the sense of fatigue and in the appreciation of weight and of resistance 

 to contraction. Their contractility and excitability are properties that 

 enable them to contract under stimulation. All these general properties 

 belong strictly to physiology, as do some special acts that are not neces- 

 sarily involved in the study of ordinary descriptive anatomy. 



Elasticity of Muscles. The true muscular substance contained in 

 the sarcolemma is eminently contractile ; and although it may possess a 

 certain degree of elasticity, this property is most strongly marked in the 

 accessory anatomical elements. The interstitial fibrous tissue is loose 

 and presents a certain number of elastic fibres ; and the sarcolemma is 

 very elastic. It is probably the sarcolemma that gives to the muscles 

 their retractile power after simple extension. 



Muscular Tonicity. The muscles, under normal conditions, have an 

 insensible and a constant tendency to contract, which is more or less 



