[cameron-brownlee] gas in TISSUES OF THE FROG 65 



weak (e.g. 0- 15 per cent.) solutions of sodium chloride (this suggestion 

 was first put forward by Durig^). and the counter possibility that 

 absorption takes place through the alimentary tract, and not through 

 the skin. He claims that his experiments show that the skin of am- 

 phibia allows salts to pass inwards, and water to pass outwards. 



Brunacci experimented on R. esculenta (with both winter and sum- 

 mer frogs.) He found that summer frogs placed in distilled water 

 (for from 3 to 8 days) did not change their skin color, had no fluid in 

 the lymph sacs, and no large amount of urine in the bladder. The 

 minimum value of the depression of the freezing point for blood was 

 0-430°. Similar frogs placed in hypertonic Ringer's solutions showed 

 an alteration of skin colour (it became greyer) and a large absorption 

 — shown especially by a large amount of a bright yellow coaigulable 

 liquid in the lymph sacs, especially in the lateral sacs, and large 

 amounts of urine. The maximum value for the freezing point de- 

 pression for the blood was 0-780°, obtained after immersion in 11 

 per cent. Ringer's solution. Generally speaking, the liquid in the 

 lymph sacs had a value for A a little higher or lower than that of the 

 surrounding medium, but always lower than that of the blood. Frogs 

 set themselves rapidly in osmotic equilibrium with their surroundings, 

 and the osmotic pressure of their blood always attained a higher 

 value or the animal died. Winter frogs withstood a 2 per cent, sodium 

 chloride solution for 24 hours, summer frogs only for 3 or 4 hours. 



Apparently, in Brunacci's experiments the frogs were not com- 

 pletely immersed. 



Finally we must refer to the recent note of M. H. Fischer^ who 

 has shown that frogs may remain for weeks after complete suppression 

 of external kidney function (by ligaturing both ureters) indicating 

 that excretion of water and urea and salts can take place through the 

 skin in the case of this animal. 



Comparing the above results with our own, we would point out 

 that numerous experiments with markedly hypotonic solutions (all 

 our experiments except those with distilled water come under this 

 category) yield no evidence of adaptation, but only of more or less 

 delayed action, and do not therefore support Backman's conclusions 

 from his own experiments with • 6 per cent, saline. The experiments 

 of Brunacci with distilled water, and those of Backman with fresh 

 water are in agreement with our own. All the results emphasise 

 the different effects with moderately hypotonic solutions and with 

 fresh or distilled water (very hypotonic). 



1 Durig, Arch. f. d. ges. Physiol., 1909, vol. Ixxxv, p. 401; quoted by Backman, 

 loc. cit. 



2 M. H. Fischer, Science, xli, p. 584, 1915. 



5 



