102 



Five fig. of dinitrophenol per milliliter was inactive; maximal ac- 

 tion was produced by double this concentration; 2,7-dinitrophe- 

 nanthrenequinone and 2,6-dinitrothymol gave results between the 

 two, while 2,4,6-triiodophenol was found to be half as active, and 

 3,5-dinitrosalicylic acid inactive. 



According to these data, the dinitronaphthol was four times 

 more active than dinitrophenol. Comparison of their action on the 

 phosphorescent emission of riboflavine showed that the same 

 quenching could be obtained with a concentration of dinitro- 

 naphthol one-fourth as great as that of dinitrophenol. 3,5-Dini- 

 trosalicylic acid was found inactive while dinitrothymol was com- 

 parable in activity to dinitrophenol. The phenanthrenequinone and 

 triiodophenol could not be evaluated, owing to their extreme in- 

 solubility in water. Ten fig. of dinitrophenol per milliliter corre- 

 sponds to a concentration of 5 X 10"* ^- ^^ ^^ t>^^^ shown in 

 the foregoing chapter, the drug can strongly quench £* in this 

 concentration, but its action fades out on further dilution. 



That the contractures observed were actually due to the de- 

 polarization of the membrane was demonstrated by Loewenstein 

 and the author, who measured the resting membrane potential 

 in isolated single muscle fibers and found it to disappear under 

 the action of dinitronaphthol, reaching the critical values at ap- 

 proximately the time when contracture began. 



To summarize the results, we can thus say that the experiments 

 supported the conclusion that nitrophenols exert their biological 

 action by interfering with E*, and that E* is involved in maintain- 

 ing the polarized state of the membrane. 



The action of dinitronaphthol on the membrane of isolated 

 muscle agreed with the symptoms caused by this drug if ingested 

 parenterally to the aninial. If 2 to 3 mg of this substance (in an 

 oUy solution) are injected into an adult mouse, the animal shows 

 no symptoms for an hour or so. Then it suddenly drops dead. A 

 few seconds later, all its muscles are found in violent contracture. 

 Death occurs, evidently, when the membrane potentials reach the 



