SECRETION AND ABSORPTION OF GAS, ETC. 127 



from air in the air-bladder. The consequence of this will 

 be that the nitrogen percentage in the air-bladder will be 

 increased, and as the total pressure within the air-bladder 

 is at any rate not less than that of the atmosphere, the 

 partial pressure or tension of the nitrogen in the air-bladder 

 will be greater than that of air, and therefore greater than 

 the nitrogen tension of the blood. The nitrogen of the air- 

 bladder will therefore follow the oxygen, and finally, there 

 will be no gas of any sort left. If the fish is much below 

 the surface the process of absorption of gas from the air- 

 bladder will be far more rapid since the partial pressures of 

 its gases will then be far above the partial pressures of the 

 corresponding gases in the atmosphere or in the water. 

 Every thirty feet of depth will increase by about an atmo- 

 sphere the pressure of the gases in the air-bladder. Thus 

 on the diffusion theory all the gas ought to disappear from 

 the air-bladder, whereas actually the gas in it remains un- 

 absorbed, or may even increase. 



When gas is from any cause introduced into any closed 

 space in the body, such as the pleural cavity or the blood- 

 vessels, absorption does actually occur, and this absorption 

 is rendered intelligible by the explanation just given on the 

 diffusion theory. The same explanation also applies to the 

 well-known fact that when the Eustachian tube is blocked 

 by catarrh a partial vacuum tends to be produced in the 

 middle ear, causing deafness from collapse of the membrana 

 tympani, etc. 



When the fish goes far below the surface of the water 

 the pressure in the air-bladder of course increases enor- 

 mously. Hence the partial .pressure of one or all of the 

 gases in the air-bladder rises high above the partial pressure 

 of the same gases in the water, particularly in the case of 

 oxygen, when the bladder contains a high percentage of the 

 latter gas. Consequently, on the diffusion theory, these 

 gases ought to be rapidly absorbed. At the great depths 

 at which some fish are caught, the partial pressures of the 

 gases in the air-bladder are enormous. To take an ex- 

 ample, in the case of a fish (Synaphobranchus pinnatus) 

 caught at a depth of 4500 feet, the gas from the air-bladder 



