8 4 



F. G. HALL. 



The methods for determining gases in water were similar to 

 those described by Birge and Juday (1911). Many of the experi- 

 ments were conducted in the field in order to study the fishes 

 in their natural habitats. Samples were taken from a boat and 

 although at first this seemed somewhat inconvenient, it was 

 later found that little difficulty accompanied the operations. 

 Temperatures, soundings, etc., were recorded at the time the 

 experiments were performed. 



FIG. i. Svvimbladder gas collecting tube. 



THE NORMAL COMPOSITION OF GASES IN THE SWIMBLADDER. 



It was of course important to know the normal composition of 

 the gases in the swimbladders of the species under investigation. 

 The gases vary with the species, with the dissolved gases in the 

 surrounding media, with varying temperatures and pressures, 

 and apparently with other factors that are not yet understood. 

 Probably, also, the degree of salinity of the water, the season 

 of the year, and the physiological condition of individual fishes 

 (influenced directly or indirectly by factors already mentioned) 

 act to produce variations in the composition of the gases found 

 normally in the swimbladder of any pa'rticular species. 



