REACTIONS OF FISHES TO ATMOSPHERIC GASES 259 



Vr. GENERAL DISCUSSION 



Previous to this series of almost a hundred experiments, we 

 spent much time in devisinjy means of applying the gradient 

 method of experimentation to our particular problems. By the 

 methods used we have ascertained that certain fishes react clearly 

 to ^^aryjng amounts of oxygen, carbon dioxide, acids, and to the 

 general effect of boiling. The possibility of more accurate, more 

 detailed, and more comprehensive work is evident, and is now 

 being undertaken in this laboratory. These experiments were 

 planned only as an introduction to the subject. 



We have noted that each species has differences in details of 

 movement and of resting but we have made no attempt to pre- 

 sent here a detailed statement of these differences. While recog- 

 nizing these differences, we have found a clear correspondence in 

 the general avoiding reactions given under certain conditions 

 Such reactions are gasping, rising to the surface, increased re- 

 spiratory activity, and turning back from the disturbing condition 

 of the water. These general characters of reaction clearly domi- 

 nate over the more specific details in the matter of successful 

 avoidance of otherwise stimulating conditions. This makes spe- 

 cific peculiarities of minor significance in the success of fishes 

 and points clearly to physiological characters comparable to 

 geiKiric, family, and ordinal characters but which bring together 

 fish in nowise taxonomically related. These groupings on the 

 basis of physiological or ecological characters have no relation 

 to groupings made on the usual bases of taxonomy. The major- 

 ity of investigators are commonly impressed with the detailed 

 structural characters of the organism and such peculiarities of 

 behavior as go with them, quite forgetting the physiological 

 processes and groupings which are clearly general in the sense 

 that they belong to whole groups of organisms (Shelf ord '12). 



While the possibility of groupings is clearly suggested by dif- 

 fering vigor of reaction on the part of different species, it is not 

 possible to outline such groups definitely on the basis of our 

 data, for reasons outlined on page 257. Furthermore such group- 

 ing!L5 may have to be based primarily on the reactions during 

 the breeding season. Reactions to solutes must be considered in 



