502 HANDBOOK OF PHYSIOLOGY. 



contain certain small amounts of pepsin and fibrin ferment, and also an 

 amylolytic ferment. 



Certain acids are also present, particularly sarco-lactic, as well as 

 acetic and formic. 



Of carbohydrates, glycogen and glucose (or maltose), also inosite. 



Nitrogenous crystalline bodies, such as kreatin,kreatinin,xanthin, 

 hypo-xanthin, or carnin, taurin, urea, in very small amount, uric acid 

 and inosinic acid. 



Salts, the chief of which is potassium phosphate. 



Muscle at Rest. 



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 condition. In the liv- 

 ing 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 ap- 

 proximating the points of attachment. It is obvious that if the muscles 

 were lax, the first part of the contraction until the muscle became tight 

 would be wasted. 



There is no doubt that even in a condition of rest Oxygen is abstracted 

 from the blood, and carbonic acid is 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. 



The reaction of living muscle in a resting or inactive condition is 

 neutral or faintly alkaline. 



In muscles which have been removed from the body, it has been found 

 that for some little time electrical currents can be demonstrated passing 

 from point to point on their surface; but as soon as the muscles die or 

 enter into rigor mortis, these currents disappear. 



The demonstration of muscle currents is usually done as follows : The frog's 

 muscles are the most convenient for experiment ; and a muscle of regular 

 shape, in which the fibres are parallel, is selected. The ends dfre cut off by 

 clean vertical cuts, and the resulting piece of muscle is called a regular muscle 

 prism. The muscle prism is insulated, and a pair of non-polarizable electrodes 

 connected with a very delicate galvanometer (fig. 317) is applied to various 

 points of the prism, and by a deflection of the needle to a greater or less extent 



