56 T. BRAILSFORD ROBERTSON. 



5. Thinking that perhaps the concentrations of these solutions 

 were somewhat too high to be altogether favorable, I made up a 

 series of six solutions with the concentration of LiNO 3 in each 



. iJT one, solution 24, was calculated so as to give a value of 

 ul\i'(n + v}~\ approximating to that in Ringer its composition 

 was .i^VLiNO, -f .O2.VNH 4 NO, + .01 5/VNaNO 3 , and the value 

 of ///[?'(//-|- r')] was 626.7. The remainder were solutions 

 containing the same concentrations of LiNO, and NaNO 3 , but 

 varying in NH 4 NO 3 concentration from .02^(24) to .02 5 A 7 (29). 

 The most favorable solution was 24, the others departing more 

 widely in the value of ?(/ \y(ii -\- ?')] from that for Ringer. 



This new calculated solution formed a really excellent sus- 

 tainer of the heart -beat, and by the addition of a trace ( i c.c. N / '40 

 to 100 c.c. solution) of Na.,CO.^ to give a favorable alkalinity, a 

 solution was obtained which was in every way as favorable a 

 medium for the heart-beat as the Ringer to which the same 

 amount of Na.,CO 3 had been added. Frogs' hearts beat in these so- 

 lutions (24 + Na 2 CO 3 and Ringer + Na 2 CO 3 ) for over two hours. 



6. Thus the facts are in favor of the hypothesis, and we see 

 that neither K, Ca or Cl ions are specific and essential for the 

 heart-beat, nor, probably, Na ions all that is necessary is to 

 obtain a properly balanced solution containing no ions (such as 

 heavy metals) which make irreversible compounds with proteids, 

 and having the most favorable value of uf\v(u -f- t')]. Such a 

 solution could be made up from any two or three salts whose 

 values of /// [?'(;/ -f 7<)] differed sufficiently widely in opposite 

 directions from the value for Ringer. It is not inconceivable, of 

 course, that a favorable heart solution may ultimately be found 

 which contains a heavy metal - - but one would not expect to 

 find such a solution having the same value of 2ij\_v(u -f- ?>)] as 

 Ringer, since the constants a and b (in the equation which I have 

 quoted) would probably be altered by the heavy metal. 



These experiments will be continued. 



7. In the course of an investigation on the influence of tempera- 

 ture upon the rate of the heart-beat in Ceriodaphnia the results 

 of which have appeared in the BIOLOGICAL BULLETIN,' I found that 

 the rate of the heart-beat in Ceriodaphnia is practically constant 



'Vol. X., p. 242 (1906). 



