JOSEPH KRAFKA, JR. 459 



Explanations of the Straight Line Temperature-Rate Relations and Op- 

 tima, Based on the Data of Facet Number and Developmental 

 Rate in Drosophila. 



In the bar-eyed mutant of Drosophila, two distinct reactions have 

 been examined in regard to the effect of temperature upon them. 

 One gives a typical straight line curve with a marked optimum at 

 29°. The other gives an exponential curve without decrease in rate 

 at the upper temperatures. From 15-27° these two curves approxi- 

 mate each other, suggesting a close similarity in the primary nature 

 of the two reactions throughout. Above 27° these two curves diverge. 

 Secondary factors have entered to retard the rate in one, and to trans- 

 form an exponential curve into a straight line. 



It is quite obvious that for the facet reaction there is no "enzyme 

 destruction," as there is no falling off in rate at the higher tempera- 

 tures. The optimum in the metamorphic curve shows that we are 

 in the range of temperature where such destruction would be expected. 

 The secondary factors then are not be to located in the principle of 

 enzyme destruction. 



It is likewise as evident that changes in viscosity of the protoplasm 

 cannot explain the differences observed in the two reactions since 

 both occur simultaneously in the same material. 



We may extend the same objections to such explanations as coag- 

 ulation of proteins, physical state of protoplasm, and allied phenomena. 



Balls' explanation of optima consisted in the more rapid accumula- 

 tion of waste products at high temperatures. The by-products of 

 metabolism retard the rate of the primary vital reactions. Their 

 experimental removal raised the optimum decidedly, but did not 

 carry it to the maximum temperature of growth as would be the case 

 were this the only explanation. 



Differential Temperature Coefficients as an Explanation of the Straight 

 Line Feature of Physiological Reaction Curves. 



The one idea of Balls that shows greater possibilities of development • 

 is that of differential temperature coefficients. Vital reactions are a 

 series of complex processes in which both chemical and physical 

 phenomena are represented. It is inconceivable that all these should 

 have the same temperature coefficients. Vernon (1895) has demon- 



