64 THE ROYAL SOCIETY OF CANADA 



kept constant by the excretion of a corresponding amount of water 

 througii the kidneys. Frogs placed in sodium chloride solutions of 

 varying concentration show less and less absorption of water until 

 with • 65 per cent, solution the increase of weight stops with an appar- 

 ent dynamic equilibrium. 



Hober characterised such animals as "homoiosmotic" as compared 

 with many others, such as sea-invertebrates and elasmobranchs, 

 which cannot maintain an osmotic equilibrium and which he according- 

 ly called "poikilosmotic." 



A number of papers have appeared recently by Backman and 

 collaborators, and by Brunacci. Unfortunately we have been unable 

 to consult the originals, in Swedish and in Italian journals respectively, 

 and have only seen the summaries in German journals^ which are 

 largely polemical with regard to priority concerning a modification of 

 Hober's application of homoiosmotic properties to the frog. 



Backman and Sundberg found that when R. temporaria (spring 

 and summer frogs which had already commenced feeding) were im- 

 mersed in fresh water only slight gains or losses of weight took place. 

 Animals immersed in 0-6 per cent, sodium chloride solution for 24 

 hours gained over 20 per cent, in weight. If subsequently placed in 

 distilled water for 24 hours, the whole of this increase was lost. If 

 now placed in • 6 per cent, sodium chloride solution again in the course 

 of 100 hours there was only a very slight increase of weight. If 

 placed in solutions of either sodium chloride or cane sugar, hypertonic 

 to the body-fluids, there was steady loss of weight. In 11 per cent, 

 cane sugar solution (in which the osmotic pressure was more than twice 

 that of frog's blood) the animals died in less than 18 hours, and had 

 lost in that time 30 per cent, of their body-weight. 



Backman concludes that his experiments show that R. temporaria 

 can live for a long time in a medium whose osmotic pressure is nearly 

 the same as that of the frog. The solution at first produced marked 

 effects, but the frog soon adapts itself to the medium and behaves in 

 normal fashion. The frog cannot live in a medium whose osmotic 

 pressure exceeds that of its own, but loses in weight and volume, 

 while its body-fluids increase in. concentration rapidly until isotonic 

 with the surrounding medium. 



He obtained similar results for toads {Bufo vulgaris) and tritons 

 {Triton cristatiis). He discusses the possibility of action on the skin 

 by the salt solution, especially as explaining the absence of absorption 

 in fresh water and the fact that absorption commences at once with 



1 Backman u.a., Zentralb. f. Physiol., 1911, vol. xxv, p. 837; Arch. f. d. ges, 

 Physiol., 1912, cxlviii, 396; 1913, cli, 52; Brunacci, Zentralb. f. Physiol., 1911, xxv. 

 1167; Arch. f. d. ges. Physiol., 1913, vol. cl, p. 87; vol. cliii, p. 366. 



