716 PHYSIOLOGY OF THE DOMESTIC ANIMALS. ■ 



curve produced in such a tetanic muscular contraction is represented in 



Fig. 282. 



Tetanic contraction requires for its production at least a greater 

 number than sixteen stimuli per second. It may thus be most readily 

 produced by the employment of a rapidly interrupted induction current. 



Tetanus may, however, also be produced by mechanical stimulation, 

 provided the impulses succeed each other with sufficient rapidity. In the 

 case of chemical stimulation tetanus is the ordinary expression of mus- 

 cular contraction. 



It is thus evident that the tetanic contraction is composed of a series 

 of vibrations of the muscular fibr-e, and, as would be expected from this 

 statement, is accompanied by the production of a musical note, the pitch 

 of the note depending upon the number of vibrations of the muscular 

 fibre. Wherever the muscle is artificially thrown into tetanus, as by the 

 action of an interrupted induced current, the number of vibrations, 

 of course, corresponds to the number of contractions, these depending 



a. 



Fig. 282.— Tetanus Produced with the Ordinary Magnetic Interrupter 

 of an Induction Machine, the Recording Surface Moving Slowly. 

 (Foster.) 



(To be read from left to right.) 

 The interrupted current being thrown in at a, the lever rises rapidly, but at 6 the muscle Teaches the 



maximum of contraction. This is continued until at c, when the current is shut off and relaxation 



commences. 



upon the number of interruptions of the current, and, as a consequence, 

 the number of vibrations of the muscle and the corresponding note pro- 

 duced have a pitch which corresponds in vibration to these data. 



When the ear is placed over a muscle which is thrown into contrac- 

 tion by means of the will a musical tone is likewise appreciated. This 

 serves to indicate that even in a single sharp contraction of a muscle 

 through the action of the will, that apparent single contraction .is made 

 up of a number of contractions, and every single muscular movement 

 of the animal body is, therefore, of the nature of a tetanus. 



The musical note heard indicates that the rate of vibration is 19.5 

 per second. 



We may now study the changes which occur in contracting muscle 

 in somewhat more detail. The most obvious is, of course, the change of 

 form. Such a change of form is represented by a decrease in the long 

 axis of a muscle, the shortening, perhaps amounting to three-fifths, of the 

 length of the muscle, with a corresponding increase in the cross diameter. 



