REACTION AND RESISTANCE OF FISHES. 245 



pecially gills in case of fishes). Osterhout ('14) has shown that 

 in plant cells alkalies increase the permeability up to death; 

 acids however at first produce a rapid decrease in permeability, 

 followed later by an increase which continues up to death. The 

 concentrations of acid used by Osterhout were .001 .V to .03 N. 

 Very low concentrations such as those used in the experiments 

 discussed here would very likely maintain a permanent decrease 

 in the permeability of the cells, and the concentrations of acid 

 in which the fresh-water fishes normally live, may thus protect 

 the fishes by decreasing the permeability of their gills and pre- 

 serving the normal reaction of the blood. Alkaline water, on 

 the other hand, does not do this for fresh-water fishes, and they 

 soon succumb in it. The results of Shelford and Powers ('15) 

 indicate that the action of alkaline water upon marine fishes is 

 to produce a normal permeability of the membranes and it may 

 be that acid water would kill these fishes by decreasing the per- 

 meability below normal. 



The effect of neutrality upon the permeability of tissues has 

 not been worked out, so far as I am aware, but since fresh-water 

 fishes, and probably marine fishes also, are negative to neutral 

 water, it must be that such water exerts a marked effect upon 

 the permeability, or some other physiological condition, in the 

 gill membranes. The negativeness of organisms to neutral 

 water indicates that they are either over-stimulated in such 

 water, or under-stimulation sets up internal disturbances. Thus 

 they may avoid it because of its non-stimulating character. It 

 may well be that in neutral water, the normal chemical reactions 

 do not go on, for acidity and alkalinity surpass all other con- 

 ditions, even temperature and concentration of reacting sub- 

 stance, in their influence upon many chemical processes. Of 

 all the catalytic agents, H and OH ions are by far the most im- 

 portant, and in their influence upon the stability of colloidal 

 systems they are unapproached by other substances (Henderson, 



'13). 



Birge and Juday ('n and '12) attempt to explain the vertical 

 distribution of the plankton in the lakes of Wisconsin and New 

 York, upon the basis of relation to oxygen and food. This 

 attempt has, it seems to me, met with little success, and they 



