324 MORRIS M. WELLS. 



II. PLAN OF EXPERIMENTATION. 



The method followed throughout in these experiments has 

 been, to introduce the fishes into water containing a constant and 

 fatal concentration of oxygen, carbon dioxide, or combination of 

 the two, and then to observe and record the reactions of the 

 fishes, during the time which elapsed between introduction and 

 death. This interval, between introduction and death, was 

 found to be the only time that could be accurately determined 

 for every species used. For this reason, it has been taken as the 

 basis for the data upon which the conclusions of the paper are 

 based. Shelford and Allee give, in their table of resistance to 

 low oxygen, the time consumed between introduction and the 

 turning of the fishes upon their backs. This method was tried 

 in the experiments herein described, but it was found that with 

 the species and conditions used, the "turning time" as they call 

 it, did not, at least in so far as could at this time be determined, 

 represent a definite and comparable time in the succumbing 

 reaction. For example, it was found, that in many instances, 

 the loss of equilibrium was a gradual and not a sudden process, 

 an illustration being the case of the rock bass (Ambloplites 

 rupestris). It was found that when two or more species were 

 compared, first, with regard to turning time, and second, with 

 regard to dying time, the comparisons did not show the same 

 relations, in the majority of cases. Furthermore the catfishes 

 and darters often died in a normal upright position, and displayed 

 at no time a reaction that might be taken as the turning point. 



It should be stated that Shelford and Allee observed their 

 fishes under conditions which varied considerably from those of 

 these experiments. They confined them in standing water, the 

 temperature of which was not constant ; the waste products were 

 allowed to accumulate; and the gas concentrations varied as a 

 result. In the following experiments, the fishes were observed 

 in running water of constant temperature, and very slightly 

 varying gas concentrations. 



For the determination of the death point, the best criterion 

 that presented itself was cessation of movement. To make 

 certain that this point might safely be taken as the death point, 

 individuals of different species were, from time to time, removed 



