80 . PHYSIOLOGY OF MUSCLE AND NERVE 



possible at this time to assign a definite cause to this reaction. Barium 

 salts, glycerin, and nicotin produce somewhat similar effects.^ 



If a muscle is placed in a 0.6 per cent, solution of sodium chlorid 

 or is frequently moistened with it, it retains its functional qualities 

 for a long time, because this fluid is practically isotonic to the myo- 

 plasm. A strong solution of this salt, on the other hand, causes the 

 muscle to twitch irregularly, either as a whole or along certain of its 

 strands of fibers. The muscle then exhibits a behavior very similar 

 to that shown by the fibrillating heart. Inasmuch as these results 

 are also obtained with sodium chlorid dissolved in distilled water, the 

 ordinary preservative fluid for muscle should be made with tap- 

 water which contains at least a trace of calcium. This salt neu- 

 tralizes the excitatory action of the sodium. More pronounced 

 stimulating effects may be obtained with solutions of Na2C03, or with 

 a solution containing 0.5 per cent. NaCl, 0.2 per cent. NaHP04 and 0.04 

 per cent. Na2C03 (Biedermann). When mixed in this proportion, 

 these salts aie capable of inducing an almost rhythmic activity of 

 skeletal muscle. Potassium salts act as depressants. Thus, even 

 normal saline solution when mixed with a few drops of potassium, will 

 induce fatigue within a very short time. Owing to this fact and be- 

 cause the ash of muscle contains a considerable amount of potassium, 

 it has been thought that the liberation of these salts during muscular 

 activity is responsible for the phenomena of fatigue. 



Fatigue. — If a fresh muscle is stimulated for some time with in- 

 duction shocks of moderate strength, the successive contractions gradu- 

 ally decrease in height but increase in length. Furthermore, if a 

 record is made of the latent period, it will be found that its length is 

 steadily increased, indicating thereby a very definite diminution in the 

 irritability of the muscle substance. This observation may also be 

 made upon a muscle which is subjected to a quickly interrupted current 

 of long duration. The height of the contraction decreases gradually 

 as the current is continued. Quite similarly, it will be noted that the 

 repeated tetanization of a muscle gives rise to curves of slowly de- 

 creasing amplitude. 



Inside the body, a muscle cannot be fatigued so easily, because its 

 waste products are constantly removed by the blood stream, while new 

 substances are brought to it to replace those which have been lost 

 during the preceding contractions. An excised muscle, on the other 

 hand, possesses only a small store of reserve material and has no 

 means of ridding itself of the fatigue substances. For this reason, 

 it shows these phenomena more promptly and never recovers com- 

 pletely from the stimulations. Its condition, however, may be ma- 

 terially improved by perfusing it with defibrinated blood or normal 

 saline solution. Contrariwise, it is possible to hasten its exhaustion 

 by perfusing it with a dilute solution of lactic acid, or with saline 

 containing a considerable amount of carbon dioxid. These two agents, 

 ^ Motinsky and Straub, Arch, fiir exp. Path. u. Pharm., li, 1904, 310. 



