300 W. C. ALLEE 



with an amount of oxygen that at first caused a decided lessen- 

 ing of the positive reaction.^ 



The second part of the table shows an interesting case of the 

 correlation between the amount of oxygen present and the posi- 

 tive response of the isopods. The first two field trials show a 

 medium amount of oxygen present and a correspondingly medium 

 positive response. The third trial shows the effects of nine days' 

 in the laboratory in which time the oxygen had been almost all 

 used and the positive response is halved as a result. Then with 

 an increase in the amount of oxygen, the positive reaction 

 increased. In both of these cases the control was furnished by 

 keeping the same animals in running water, and as was seen in 

 table 2, those isopods stayed positive throughout as far as oxygen 

 was concerned. 



In the next two parts of the table, however, the control was 

 kept under exactly the same conditions as the experiment, except 

 as regards the oxygen content. Part 3 shows both the acclimati- 

 zation effect and the dependence of the positive reaction upon the 

 amount of oxygen present. Part 4 gives some idea as to the rate 

 with which the effect of a lowered amount of oxygen may be 

 reflected in the rheota.ctic response. 



The amount of carbon dioxide free in the water was never high 

 in these experiments. The highest record is that of 4.5 cc. per 

 liter which occurred in the experiment given in part 1 of the table. 

 In the last experiment given, the carbon dioxide did not rise 

 above 1 cc. per liter in the experiment while in the control it was 

 between 1 and 3 cc. to the liter. Neither can the boiled water 

 have been a factor in these changes, for the isopods used in the 

 last case, both control and experiment, had been kept for a month 

 in the boiled water that had been saturated with oxygen by ab- 

 sorption from the air.. For that matter, the reactions given in 

 table 1 were given by isopods from this reaerated boiled water, 

 and it will be remembered that their reactions averaged 89.4 

 per cent positive. 



^ Haldane and Smith ('97, p. 250) report a similar acclimatization occurring in 

 mice when subjected to a decreased oxygen tension. 



