101 



of the membrane following excitation was thus not affected by 

 the dinitronaphthol. (This rapid repolarization can be slowed 

 down by substances, such as cyanide, which cut out the whole 

 energy supply.) The dinitronaphthol seems to have acted on some 



Fig. 25. Dinitrophenol contracture of isolated rat diaphragm muscle, 

 a: Nerve stimulated with a frequency of 12 impulses per minute, b: Same 

 with one stimulus per minute. At arrow 2.57 dinitronaphthol were added 

 per milliliter. 



slower process, interfering, possibly, with the energy supply which 

 is needed for the maintenance of the normal structure of the mem- 

 brane or its pumping action. 



Whatever the nature of the action of the dinitronaphthol may 

 be, we can expect that it acts in an "all-or-none" fashion, that is, 

 produces contracture if it diminishes the potential to its critical 

 value, or produces no action at all. The experiment showed dini- 

 tronaphthol to be inactive in a concentration of 1.25 /tg. per milli- 

 liter, while 2.5 /j^g. per milliliter produced maximal contracture. 



