112 



F. G. HALL. 



TABLE XII. 



DETERMINATIONS OF THE pH OF THE SWIMBLADDER GLAND OF PERCH SUBJECTED 



TO AN INCREASED PRESSURE. 



These were made similar to those described in Table XI. The "duration of 

 stimulus" indicates the time to which fishes were subjected to external pressure. 



in the acidity is evidently produced in the epithelial cells and 

 acid dialyzes into the capillaries. Two things may be produced 

 in the capillaries: (i). an increase in the calibre of the capillaries; 

 (2) a more complete dissociation of oxygen from oxy-hemoglobin. 

 In either case more oxygen would be furnished to the gland. 

 By increasing the calibre of the blood vessels more blood is 

 brought to the gland and by a more complete oxygen dissociation 

 a greater oxygen tension results. It is not possible to account 

 for the greater oxygen tension in the swimbladder by the first 

 means; by the second, however, where the local tension of oxygen 

 might be so high, it is possible to see how the oxygen tension in 

 the swimbladder might be considerably higher than in the 

 general arterial system. If this hypothesis be correct it is easy 

 to undersrand the purpose of the great mass of capillaries. The 

 function on the thick layer of epithelium is also explained. 

 Just what the nature of the effective acid is can not be stated at 

 present. Perhaps further investigation will reveal its character. 

 Another observation which seems to support the view just 

 proposed relates to the change in size which the gland undergoes. 

 It is noticeable that there is an increase in the size of the swim- 

 bladder glands that have been stimulated. They also appear 

 redder in color. The increase in size is evidenced also by the 

 increase in weight shown in Tables IX. XII. The average 



