A DEGENERATE GLAND. — PRINCE. 201 



It is important at this point to notice the nature of tlie 

 gaseous contents of the swim-blackler, so far as these have been 

 ascertained. Most of the older authorities declared that it was 

 filled with air, although Provencal and Humboldt, nearly a 

 hundred years ago (it was in 1809), published an analysis whicli 

 showed that, in some cases, oxygen filled the sac, while in other 

 examples only 1% to 5^ of the contents consisted of oxygen, 

 and the greater portion was nitrogen. They thought that the 

 oxygen increased with the depth of the fish's habitat, a view 

 whicli later investigations have jDroved to be erroneous. In the 

 fishes, for instance, brought up from the greatest depths of the 

 sea, during the cruise of H. M. S. " Challenger;" very little 

 oxygen was found in the swim-bladder, while in specimens 

 frequenting the surface waters that gas formed quite a con- 

 siderable percentage. (No. 4, Vol. I, p. 226). Fish from a 

 depth of 2875 fathoms showed not more than 4^ to 5^ of 

 oxygen in the swim -bladder, but, at the surface, specimens of 

 fish were found to have 34% or 35% of oxygen in the gaseous 

 contents of the organ. Configliacchio and Biot discovered a 

 large proportion of oxygen in specimens from fairly deep water, 

 and the most recent authority on the subject (Professor R. \V. 

 Tower, of Brown University, U. S. A.), states that at a depth 

 of from 35 to 70 fathoms the walls of the swim-bladder secrete 

 oxygen very actively. The organ has nervous branches, gastric 

 filaments, from the Vagus nerve, as well as a sympatlietic supply, 

 and, according to Bohr's experiments, division of the tenth nerve 

 stops all secretion of gas, while section of the sympathetic nerve 

 hastens the secretion of gas. Dr. Giinther (No. 9, p. 142) has 

 stated that, in fresh-water species, little oxygen gas as a rule is 

 found, nitrogen prevailing, with just a trace of carbonic acid ; 

 biit in sea-fishes the amount of oxygen is much larger. In a 

 fresh-run salmon Dr. John Davy found 10% of oxygen, a trace 

 of carbonic acid, and nearly 90% of nitrogen, an observation 

 of a remarkable nature as the fish had only just left the sea, 

 probably. All observations tend to show that there is no 



