OXYGEN. 433 



A very considerable secretion of gases takes place in the swimming- 

 bladder of fishes. Biot, 1 who examined the gases in fishes which live at 

 great depths, found sometimes as much as 80 per cent of oxygen. Whereas 

 the oxygen tension of water at a depth of, say, 1500 meters, amounts to 

 only about one-fifth of an atmosphere, the partial pressure of this gas in 

 the swimming-bladder is equivalent to that of 90 atmospheres. Moreau 2 

 has shown, moreover, that the oxygen content of these gases in the swim- 

 ming-bladders of fish depends upon the depth at which the fish lives. 

 Those living near the top of the water often contain a lower oxygen pressure 

 than that of the atmosphere. If the same fish be placed at a greater depth, 

 it is no longer in equilibrium with its surroundings. Equilibrium is 

 restored, however, by more oxygen being secreted in the swimming-bladder. 

 If the bladder is emptied by means of a trocar, it refills with oxygen after 

 a time. This secretion, furthermore, is under the influence of the nervous 

 system. On severing the pneumogastric (vagus) nerve, the gas secretion 

 entirely ceases. Then, on artificially emptying the swimming-bladder, 

 it does not refill with oxygen. The epithelium of the bladder itself is 

 impermeable to oxygen. The oxygen passes out through the so-called 

 oval. 



These observations are sufficient to prove beyond question that the 

 animal organism possesses cells whose function it is to secrete gases. It is 

 true that these results cannot be applied immediately to higher organisms, 

 but it gives undoubted support to Bohr's opinions. 3 By means of this 

 active taking up of oxygen, the animal organism obtains a certain supply 

 of this important gas, so that air containing but little oxygen suffices for 

 its support within certain limits. Thus, for example, muscular effort 

 requires an increased oxygen supply by an increase in the blood circula- 

 tion. In a unit of time more blood passes through the lungs. If, by an 

 artificial restriction of one of the pulmonary branches, more blood is made 

 to pass through one lung than through the other, there is more oxygen 

 taken up in the lung with the more blood, although the effect upon the 

 elimination of carbon dioxide is not so marked. 4 



An interesting question, but one not so easy to answer, is whether the 

 lungs of mammals are dependent upon certain nervous influences. This 

 is known to be true in the case of the tortoise. With the Testudo grceca, 

 the trachea divides so high up in the neck that, without fear of injuring 

 the important nerves, cannulas may be placed in the bronchi, and thus 

 either lung be observed independently. If the vagus branches to one lung 

 are cut, the absorption of oxygen by that lung is lessened, while that of 



1 Me"moires de la societe d'Arcueil, 1807. 



2 Memoires de Physiologie. Paris, 1877. 

 8 C. Bohr: J. Physiol. 15, 494 (1894). 



4 V. Maar: Skand. Arch. Physiol. 15, 1 (1903); 16, 358 (1904). 



