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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



during the cooling process a striated muscle of a frog be irritated from time to 

 time with single induction shocks, the height of the contractions does not con- 

 tinually grow less as one would expect. 1 The maximal height is obtained at 

 30 C., the height above this point being somewhat less, the irritability les- 

 sening as the coagulation-point is approached ; from 30 C. to 19 C. the 

 height continually decreases, but from 19 to C. the height increases, while 

 below C. it again becomes less, until at the freezing-point of muscle no con- 

 traction is obtained. The cause of these peculiar phenomena is not definitely 

 understood. 



FIG. 56. Schema of effect of temperature on height and form of contraction curve : a, contraction at 

 19 C. ; 6, c, d, e, f, contractions made at intervals, each one at a lower temperature ; g, h, contractions 

 at higher temperatures than 19 C., h being made when the temperature was 30 C. ; i, k, I, show a different 

 series of contractions, made as the temperature was increased from 30 C. toward the point at which the 

 muscle-substance coagulates (after Gad and Heymans). 



(/) Effect of Drugs and Chemicals upon Muscular Contraction. Certain drugs 

 and chemicals have a marked eifect upon the irritability and conductivity of 

 muscles, and these effects must necessarily find expression in the amount of con- 

 traction which would be excited by a given irritant. In addition to this, it is 

 worthy of notice that the character of the contraction may be altered. 



The drug which has the most striking effect upon the form of contraction is 

 veratria. A few drops of a one per cent, solution of the acetate of veratria, in- 

 jected beneath the skin of a frog whose brain has first been destroyed, in a few 

 minutes alters completely the character of the reflex movements ; the muscles 



FIG. 57. Myogram of muscle poisoned with veratria and that of a normal muscle : a, myogram from a 

 normal gastrocnemius muscle of a frog the waves at the close are due to the recoil of the recording lever ; 

 6, myogram from a gastrocnemius muscle poisoned with veratria, recorded at the same part of the drum. 



are still capable of rapidly contracting, but the contractions are cramp-like, 

 the power to relax being greatly lessened. The poison acts upon the muscle- 

 substance. If a muscle poisoned with veratria be isolated and connected with 

 1 Gad und Heymans: Archivfiir Anatomic und Physiologic, 1890, p. 73. 



