1910.] Comparative Toxicity of Theobromine and Caffeine. 571 



The concentrations are in the ratio 1:1-5:2 and the times are in the ratio 

 3:2:1, with an error of 0-5 minute, which is that of experiment. 



Fig. 1.— Caffeine, ?i/200 (Ol per cent.). Fig. 2.— Theobromine, m/200 (0-09 per 



cent.). 



On comparing theobromine and caffeine solutions of like concentration, 

 namely, ?i/200 (which was actually done simultaneously with a pair of 

 muscles), the times required for abolition are in the ratio 6"5 : 11 or 1 : 17 ; 

 again, on comparing a n/'30O solution of theobromine with a n/200 solution of 

 caffeine the times are in the ratio 9 : 11 or 1 : 1-2; which would be nearly 

 equivalent to a ratio 1 : 1*8 in terms of the same concentration. From these 

 results we conclude that the toxic value of theobromine is to that of caffeine 

 approximately as 1-7:1 for equal molecules or 1-8:1 for equal weights. It 

 appears that the introduction of the methyl group into theobromine to form 

 caffeine lowers the toxic value, a result which is the converse of that obtained 

 in the case of the paraffinoid alcohols* and unlike those of methyl stovaine 

 and stovaine.f and of pyridine and picoline,| in which such introduction of a 

 methyl group produced approximately no alteration of activity. 



Coffee and Tea Extracts. 



We also made a few observations with ordinary extracts of coffee, with and 

 without caffeine, and of tea ; herein we are indebted to the Life Belt Coffee 

 Company, Ltd., for supplying us with samples of " coffee freed from caffeine " ; 

 it appears from the analyses given that by the process adopted 90 per cent., or 

 thereabouts, of the caffeine is removed. For the purposes of these experiments 

 we made our " tea " and " coffee " by boiling in physiological saline solution 

 in the proportion of 2-5 and 5 grammes per 100 c.c, filtering off the solid 

 matter and using the extracts. In order to determine the amount of solid 

 dissolved under such conditions 50 c.c. of the 5 per cent, extracts were 

 evaporated to dryness and the residue weighed. After deduction of the 



* Kemp, ' Journ. Physiol.,' 1908, vol. :37, p. 43. 



t Veley and Waller, ' Proc. Eoy. Soc.,' B, 1910, vol. 82, p. 147. 



X Ibid., p. 336. 



