314 ELLINOR HELENE BEHRE. 



3. Estimations of CC>2 production by a colorimetric method 

 and by the Tashiro biometer give essentially the same results 

 as the susceptibility method. The increase in CO" production 

 which occurs when animals are brought from a lower to a higher 

 temperature is followed by a gradual decrease at the higher tem- 

 perature; and the decrease in CC>2 production which occurs when 

 animals are brought from a higher temperature is followed by a 

 gradual increase in CC>2 production at the lower temperature. 



4. Experiments on the effect of temperature on head-frequency 

 in the regulation of pieces give results similar to those on suscepti- 

 bility and on CC>2 production. Rise in temperature increases, 

 fall in temperature decreases, head-frequency, but acclimation 

 determines changes in head-frequency in opposite directions 

 from those directly determined by change of temperature. 

 Animals which have become acclimated to a high temperature 

 show a lower head-frequency in regulation than those brought 

 into that temperature at the beginning of regulation ; and animals 

 acclimated to low temperature show r a higher head-frequency 

 than those brought into that temperature at the beginning of 

 regulation. 



5. All the experimental data agree in indicating that, within 

 the temperature range of the experiments, acclimation to a 

 change in temperature upward consists in changes which manifest 

 themselves physiologically as a gradual decrease in rate of meta- 

 bolism or oxidation; and acclimation to a change in temperature 

 downward consists in changes which manifest themselves physio- 

 logically as a gradual increase in rate of metabolism or oxidation. 



6. The working of the regulating mechanism concerned in 

 acclimation to temperature resembles as regards its action on 

 metabolism the temperature-regulating mechanism of warm- 

 blooded animals, but is very much slower and less effective as a 

 compensatory mechanism than the latter. It may perhaps be 

 regarded as representing the general basis from which a tempera- 

 ture-regulating mechanism has developed. 



