50 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



nients employed to record the contraction of a muscle is called a myograph, and 

 the record of the contraction is termed a myogram. If, when the muscle of a 

 nerve-muscle preparation is thus arranged to write its 



( T ' contractions, the nerve be irritated with alternating mak- 



ing and breaking induction shocks of medium strength, 

 the muscle will make a series of movements, which, if 

 the surface be moved past the writing-point a short 

 distance after each contraction, will be pictured in the 



FIG. i4.-Effect of making record as a row of alternating long and short lines, the 

 and breaking induction records of the breaking contractions being higher than 

 those of the making contractions (Fig. 14). Similar 



results are obtained if, instead of irritating the nerve, we irritate the curarized 

 muscle directly. 



Stimulating Effects of Making and Breaking the Direct Battery Current. 

 On account of the construction of the induction apparatus, breaking induction 

 shocks are more effective stimuli than making induction shocks. The reverse 

 is true of the stimulating effects which come from making and breaking the 

 direct battery current. The excitation which results from sending a galvanic 

 current into a nerve or muscle is stronger than that which is caused by the 

 withdrawal of the current. This difference is due to the physiological altera- 

 tions produced by the current as it flows through the irritable substance, and 

 is without doubt closely associated with changes in the irritability which occur 

 at the moment of the entrance and exit of the current. 



The making contraction starts from the kathode, and the breaking contraction 

 from the anode. The irritation process which results from making the current 

 is developed at the kathode, and that which results from breaking the current 

 is developed at the anode. This was first demonstrated on normal muscles by 

 Von Bezold, 1 and has since been substantiated for nerves as well as muscles 



FIG. 15. Schema of Bering's double myograph : C, clamp holding middle of muscle ; P,P, pulleys to 

 the axes of which the recording levers are attached ; p,p, pulleys for the light weights which keep the 

 muscle under slight tension ; A, positive electrode ; K, negative electrode ; r, commutator for reversing 

 the current ; k, key ; 6, battery. 



by the experiments of a great many observers. Perhaps the most striking 

 demonstration is to be obtained by Engelmann's method. The positive and 

 negative electrodes are applied to the two extremities of a long curarized sarto- 



1 Untersuchungen uber die dektrische Erregung von Muskeln und Nerven, 1861. 



