104 F - G. HALL. 



In the carp, however, which has a duct from the swimbladder 

 opening into the pharynx, no such, tension difference could be 

 detected. Physical diffusion probably accounts for the passage 

 of gases to and from the swimbladder in this fish. 



In the normal bass living at the surface, where little or no 

 depth changes are taking place, the percentage of the gases in 

 the swimbladder is probably controlled by simple diffusion. 

 For when determinations were made on such bass the tension 

 of the swimbladder gases and the blood appeared to be the same. 

 It is only when changes such as pressure made a rapid increase 

 of gases in the swimbladder necessary that secretion operated. 



DISCUSSION. 



The results of this investigation show that in the swimbladder 

 of fishes an active secretion of gases exists, especially of oxygen. 

 There apparently is a regulatory mechanism by which fishes can 

 adjust their specific gravity to that of the environment, thus 

 enabling them to maintain themselves at any particular level 

 with a minimum expenditure of energy. What is this mechanism ? 

 Gas secretion has been an extremely controversial subject, 

 especially when reference is made to the lung of the higher 

 vertebrates and the swimbladder has been considered by many 

 to be the homologue of the lung. 



It is quite apparent that the gases of the swimbladder are 

 derived from the blood. Oxygen plays the more active role in 

 this secretion and nitrogen, which is more inert, is more passive. 

 This at first may seem strange, but if a gas is to be secreted from 

 the blood or absorbed by the blood the advantages are obvious. 

 Oxygen can be easily obtained from oxy-hemolobin and can be 

 used up either by combination with reduced hemoglobin or by 

 oxidation of some reducing substance. 



In the mechanism by which the swimbladder derives its 

 oxygen two provisions are necessary: first, the provision for 

 bringing the quantity of oxygen which is required; second, the 

 process by which the oxygen is transferred from the capillary 

 blood vessels to the swimbladder. 



