[cameron-browxNlee] low TEMPERATURES ON THE FROG 111 



There is close agreement therefore between the death-point of 

 the muscles of two different species of frogs, R. fusca and R. escule^ita. 

 Experiments on frogs' nerves have shown on the other hand that 

 marked differences may exist with different species. According to 

 Boycott* the frog's nerve conducts well up to the moment of freezing. 

 He found that the lowest temperature at which conductivity takes place 

 is 7°. Biihler's results are in good agreement. f Howell, Budget, and 

 Leonhard+ obtained the remarka]:)le result that sometimes in spring 

 nerve-irritability was lost at -\-ô° or even at -l-lo°C. Garten and Sulze 

 have recently studied side by side R. csculenta and the Indian frog, 

 R. hexadactyla.* They find that in the sciatic nerve of the latter ir- 

 ritability ceases at -|-5°, while in R. esculenta stimulation at -9° still 

 produces an effect. 



It would therefore appear from these experiments that there are 

 marked differences in the temperature effect on the nerves of frogs from 

 tropical and temperate climates, and further that the death-point of 

 the sciatic nerve of R. esculenta is certainly below -9°, since the freez- 

 ing-point is below this; results with muscle suggest that the death- 

 point will lie distinctly lower than the freezing-point. 



We have found from repeated experiments that a frog freezes in a 

 manner very similar to that of a corresponding amount of saline iso- 

 tonic with its blood. This is clearl}^ shown by the curves in figure 1, 

 corresponding to experiment 13. In this experiment a frog had the bulb 

 of a small thermometer inserted into the stomach through the gullet. 

 In a small' beaker of water an equal amount of Ringer's solution was 

 placed and a similar thermometer placed within it. Both vessels were 

 subjected to an almost constant external temperature of about -10°. 

 In the figure time and internal temperature are plotted against each 

 other. It will be observed, as might be expected, that the freezing 

 points of the two solutions are identical. The frog freezes more rapidly. 

 This is probably to be attributed to the smaller amount of fluid and the 

 much greater surface. Nevertheless a very considerable time elapses 

 before freezing is complete and the temperature commences to fall 

 further. This clearly gives a clue to the results of Mr. Mann's experi- 

 ments (p. 109j and explains those of Professor Fraser Harris. Mr. 

 Mann's results do not indicate in any way the actual internal tempera- 



*"0n the influence of temperature on the conductivity of nerve," J. Physiol., 

 27, 488, 1902. Cp. aso. Tait, Proc. Physiol. Soc, xxxv-vi, J. Physiol., 34, 1906. 



t "Ueber den Einfluss tiefer Temperaturen auf die Leitfàhigkeit des motorischen 

 Froschnerven," Engelmann's Archiv., 1905, p. 239. 



X "The effect of stimulation and of changes of temperature upon the irritability 

 and conductivity of nerve fibres," J. Physiol., 16, 298, 1894. 



* "Ueber den Einfluss niederer Temperatur auf die Nerven einer tropischen 

 Kaltblukers {Rana hexadadylct) ," Z. Bio!., 60, 163, 1913. 



