A. T. CAMERON AND M. S. HOLLENBERG 413 



dent as a chloride-Ringer solution. Macht and Hooker (1918) have 

 shown that perfusion of the medulla of a mammal by a bromide 

 solution stimulates the respiratory and cardio-inhibitory centers. 

 Kruse considers therefore that the bromides are more or less irritat- 

 ing to most tissues of the body, but states that the central nervous 

 system of the frog is not depressed by sodium bromide. 



Stiles (1901) showed that isolated strips of frog esophagus are 

 maintained in rhythm by bromide-Ringer solution. Prochnow (191 1) 

 has shown that the sodium halides increase the tonus of the uterus 

 and the smooth muscle of arteries in the order, NaF, Nal, NaBr, 

 the excitability being increased. Kruse found that bromides stimu- 

 lated smooth muscle (intestine of dog or cat) slightly under normal 

 conditions, and markedly when arrhythmic or fatigued. 



Greisheimer (1919) found that m/8 sodium bromide is more toxic 

 than m/8 sodiimi chloride as judged by the effect on the motor nerve 

 of the frog. 



Finckh (1921) has tested the effects of sodium halides on the isolated 

 frog heart. In bromide-Ringer solution the heart continues beating 

 for a long time, whence Finckh concludes that the chloride ion plays 

 no peculiar role in this connection. When iodide-Ringer solution 

 is substituted, harmful effects are observed which are attributed 

 to the formation of elementary iodine. Nitrate-Ringer solution gives 

 a similar result; here the toxic effect is explained by the possible forma- 

 tion of NO2 ions. ' 



Experimental. 



We have determined the survival periods of frog heart and gastroc- 

 nemius-sciatic preparations {Rana pipiens) immersed in modified 

 Locke solutions in which varying amounts of sodium chloride were 

 replaced by the corresponding molecular concentrations of the sodium 

 salts of the anions studied, fluoride, bromide, iodide, chlorate, iodate, 

 and nitrate (Table I) . In each set of experiments the solutions were 

 made up with freshly distilled water, and the preparations, dis- 

 sected as quickly as possible, were immersed in them in shallow ves- 

 sels, so that the oxygen supply could be regarded as sufficient. The 

 volume of solution, compared to volume of tissue, was large. From 

 time to time the preparations were observed and tested. The times 



