28 PHYSIOLOGY OF MUSCLES A:SD NERVES. 



CHAPTER III. 



1. Irritability of muscle ; 2. Contraction and tetanus ; 3. Height 

 of elevation and performance of work ; 4. Internal work during 

 tetanus; 5. Generation of heat and muscle-tone ; 6. Alteration 

 in form during contraction. 



o 



1. If a muscle is cut from the body of a frog, and 

 is fastened into the myograph just described, it never 

 shortens spontaneously. If this does seem to happen, it 

 may safely be assumed that some accidental and un- 

 perceived external cause has influenced it. A muscle 

 may, however, always be induced to shorten by 

 pinching it with tweezers, by smearing it with strong 

 acid, or by bringing certain other external influences, 

 the nature of which we shall presently learn, to bear 

 upon it. Muscle, therefore, never shortens sponta- 

 neously, but it can always be induced to do so. This 

 quality of muscle enables us to produce the state 

 of contraction at pleasure^ and to examine accurately 

 the nature and method of the conditions which give 

 rise to it and the phenomena by which it is accom- 

 panied. 



The myograph which, by means of the indicator 

 attached to it, marks the contraction of the muscle on 

 the smoked glass plate, and at the same time affords 

 opportunity for measuring the extent of the contraction, 

 will presently prove of yet greater service. But for 



