No. 614] PHYSIOLOGICAL PROBLEMS 



133 



ments and citations below are in support of this state- 

 ment. 



(a) Temperature Threshold 

 Very nearly at the time of the publication of Krogh's 

 work, Sanderson and Peairs announced that for a large 

 series of insects the time-temperature curve for develop- 

 ment is a hyperbola and the velocity of development 

 curve is a straight line. Peairs concluded further that 

 the (reciprocal) relative velocity curve which is obtained 

 by dividing unity (100 to avoid fractions) by the experi- 

 mentally determined time periods, in days or other units, 

 and plotting it against the temperature for which the time 

 was observed, gives points for the different temperatures 

 which fall in a straight line crossing the axis of tempera- 

 ture at the zero of the curve, or the theoretical threshold 

 of development (Fig. 1). This theoretical threshold maybe 

 calculated also with two points accurately determined ex- 

 perimentally. These authors conclude that with the zero 

 determined, the thermal constant (temperature multiplied 

 by time— a constant for an hyperbola) can be obtained. 

 However, they failed to note the deviations from law 

 which occur at both high and low temperatures and which 

 require careful attention in practical work. 



These entomological workers appear to have over- 

 looked the work of the fish culturists who have studied 

 the subject of effects of temperature on development. 

 Apstein ('11), Dannevig ('91), Earll ('78), Green (70), 

 Johansen and Krogh ('14), Reibisch ('02), and William- 

 son ('08) all made contributions of greater or less im- 

 portance. All called attention to the effect of tempera- 



