336 MORRIS M. WELLS. 



young were averaged with the adults, the fishes were divided 

 into two groups upon the basis of weight. The dividing line 

 between the groups fell more or less naturally at about 5 grams. 

 Upon calculating the data for the two groups thus formed, it 

 was further found that each group illustrated much the same 

 specific relations, and for this reason but one group, that of the 

 larger or adult fishes, will be discussed. In Table IV. is indi- 

 cated the resistance of a number of species to different experi- 

 mental conditions. 



Table IV. illustrates the following points: (i) the relative 

 specific resistance of the fishes to the six artificial environments 

 taken singly (vertical columns, except last two) ; (2) the relative 

 specific resistance of the fishes to the environments taken together 

 (last two vertical columns) ; (3) the efficiency of each environ- 

 ment as a death-producer for the species used; (4) the antagon- 

 istic action of oxygen and carbon dioxide when in the same 

 solution (vertical columns 5 and 6) ; (5) that an optimum carbon 

 dioxide concentration probably exists for the fishes in question 

 (columns 2 and 4); and (6) that of the concentrations used, the 

 low oxygen was more detrimental to the fishes than the high 

 carbon dioxide (columns I and 3). 



With regard to the relative resistance of the different species 

 to the environments taken singly, attention is called to the 

 fact that the order varied with the different combinations. 

 This indicates that fish species vary in their resistance to any 

 one factor, the species that is more resistant in one environment 

 being less so in another. The relative resistance of the species 

 to the environments taken as a whole is shown in the last two 

 columns. The order was obtained by averaging the resistances 

 to the single environments. Reading from right to left along 

 nearly any horizontal row of figures will show an increasing 

 resistance of the species to the different environments as arranged 

 in the table. The most fatal combination used was low oxygen 

 (0.1-0.15 c.c. per 1.) and high carbon dioxide (35-50 c.c. per 1.), 

 and the least fatal, high oxygen (8-10 c.c. per 1.) and high carbon 

 dioxide. That this would be the result has already been inti- 

 mated by Shelford and Alice ('13). 



If in the table, column 5 be compared with column 6, it will be 



