22 THE NEW PHYSIOLOGY. 



scope, the presence of one or more gas-bubbles inside 

 its protoplasm can at times be observed, particularly 

 if by accident or design the animal has been turned 

 on its back, with the opening of its shell upwards. The 

 bubbles of course make the animal lighter, so that it 

 rises towards the surface of the water, and also comes 

 right side up, after which they rapidly disappear again. 

 The occurrence of these phenomena was described many 

 years ago by Engelmann. Quite recently Dr Bles took 

 up the subject again at my suggestion, and elicited the 

 very interesting fact that a comparatively slight de- 

 ficiency in the normal oxygen percentage of the water 

 causes the animal to develop bubbles at once, and 

 come to the surface. 



Now this is apparently a case of visible and easily 

 observed intra-protoplasmic gas-secretion, and for vari- 

 ous reasons it is probable that the gas liberated is oxy- 

 gen. The occurrence of oxygen-secretion was already 

 known, as an isolated fact, in the case of the swim- 

 bladder of the fishes. The original discovery of this 

 was made over one hundred years ago by the French 

 physicist and chemist Biot. Being engaged in some sur- 

 vey work on the Mediterranean, he was attracted by the 

 observation that deep-sea fishes caught with a line at 

 great depths come to the surface with their swim- 

 bladders distended with gas, or even bursting. Led by a 

 sure scientific instinct, he determined to analyse the gas, 

 but expected it to be something like air in composition. 

 He added hydrogen to some of the gas in a eudiometer 

 and passed a spark, in order to determine the oxygen 

 in the usual way. But instead of the ordinary mild 

 explosion in analyses of air there was a violent explosion 



