NOTES. 443 



cannot gulp the air, they soon die, even when an ample supply of highly 

 aerated water is constantly added ; frogs, on the contrary, it is almost 

 impossible to kill in this way. This, however, depends to a great extent 

 on the temperature. The lower the temperature the greater is the 

 fish's power of resistance. 



J^ote 74, page 173. Bert's experiments were extremely interesting. 

 He proved that at a temperature varying between 0° and 13° C. the 

 oxygen held in the water sufficed frogs for a considerable time, for 

 they need but little. At 19' C. (water temperature) a frog died in 36 

 hours when enclosed in a bladder which contained almost iive litres (less 

 than five quarts) of water ; the frog had absorbed all the oxygen con- 

 tained in the water, as was proved by analysis. This shows that at 

 19° C. the requirements of the frog are very high. The Axolotl 

 (^Siredon mexiaaiius) can endure not merely the excision of the gills 

 but even the complete removal of its lungs, so that in this animal, as in 

 the frog, respiration by lungs and gills can be perfectly replaced by 

 respiration through the skin. I will also observe, incidentally, that it 

 does not appear to me to be clearly proved that those Amphibia which 

 are provided with both lungs and branchiaa — as Slredon, Menohranclais, 

 Meiwpmiia, &c. — do actually breathe through their lungs ; i.e. that the 

 air they gulp in through their mouth is distributed to the lungs. The 

 anatomical structure of the glottis does not seem to me particularly to 

 support this assumption. May not their lungs correspond physiologi- 

 cally rather to the air-bladders of fishes 1 (See Note 75.) 



Note 75, 2)age 173. Since the publication in 1857 of Milne- 

 Edwards's great work, which treats of the processes and organs of 

 respiration in animals, some newer and not unimportant works have 

 appeared. Emery suggests the question whether Amphibia may not store 

 up oxygen in their lungs, as it has been demonstrated that fishes do in 

 their air-bladders. Grehant shows that a fish absorbs the oxygen normally 

 existing in its air-bladder when it is kept in water of the temperature 

 of the air. Moreau asserts that the amount of oxygen contained in the 

 air-bladder increases with an increase of the action of the air-bladder ; a 

 tench, in which he tied up the air-passage leading to the air-bladder, at 

 the end of a fortnight had in it more than the normal proportion of 

 oxygen. Dividing the sympathetic nerve causes the amount of oxygen 

 deposited in the air-bladder to augment continually. Puncturing the 

 air-bladder occasions at first an increased deposition of oxygen. The 

 researches of Gouriet confirm these statements of Moreau ; they were, 

 however, instituted rather with the object of detecting the value of the 

 air-bladder as determining the swimming motions of the fish. In a 

 few cases the air-bladder of fishes seems actually to exercise tlie 

 function of lungs. Mr. Burt G. Wilder (Proe. Amer. Ass. Adv. So. 

 1875) showed that it is very probable that the spongy air-bladder of 

 Amia calva and of Lepidosteus ossevs acts as true lungs, and he has 



