FUNCTIONS OF SWIMBLADDER OF FISHES. IOI 



or tensions of the oxygen in the swimbladder and in the blood 

 coming to the swimbladder he will have the solution of the 

 problem. If the tension of the gases should be the same in the 

 swimbladder and in the blood coming to the swimbladder one 

 could but conclude that the gases were transferred by physical 

 diffusion, but if the tensions were not equal and should be 

 markedly greater on one side than on the other he would be 

 justified in concluding that an active secretion existed. 



However, the determination of the gaseous tensions in the 

 blood presents considerable difficulty. It is necessary to bring 

 the blood in contact with gaseous mixtures containing various 

 proportions of the gas whose tension in the blood it is desired to 

 measure. By making various experiments a gaseous mixture 

 will be found with which the blood is in equilibrium. For such 

 determinations an aerotonometer is used. Because fish blood 

 is somewhat difficult to handle and because of the small amounts 

 that are usually obtained the aerotonometer has not been found 

 practicable. Another method has been devised which is very 

 similar in principle to that of the aerotonometer although 

 .absolute tensions can not be determined, but rather differences 

 in tensions. However, the results are definite and strictly 

 comparable. 



A diagram of the apparatus used is shown in Fig. 7. An 

 equilibration chamber C, opening at one end through a single 

 way stopcock, I, and on the other through a three-way stopcock, 

 2, was connected to a levelling bulb, L, by rubber pressure tubing. 

 A vertical glass tube, G, was inserted in the rubber tube to make 

 visible the column of mercury within. The equilibration chamber 

 could be shifted so that the stopcock, 2, was down (position A) 

 or so that it was up (position B). T represents the position of 

 a test tube during the experiment and B a constant temperature 

 water bath surrounding the test tube. 



Gas from the swimbladder of the bass which was known to 

 have a high oxygen tension was drawn into the equilibration 

 chamber, C, through a hypodermic needle, by filling the entire 

 apparatus with mercury previously and by lowering the levelling 

 bulb, L, with the equilibration chamber in position B until the 

 mercury column could be seen in the tube G. 



Blood was drawn from the dorsal aorta of the bass under par- 



