THE INFLUENCE OF PHYSICAL FACTORS 



97 



up to a maximum at and above which the temperature has a deleterious 

 effect upon the organism. The maximum temperature probably 

 differs considerably for different animals, but very few determinations 

 have been made so far. 



The more rigorously standard conditions are maintained the more 

 regular is the influence of temperature observed. Attempts have 

 been made by Kanitz [1907], Snyder [1908], Putter [I9I4]> and 

 others to represent the temperature influence on the respiratory ex- 

 change as governed by the rule of van't Hoff, which has been found 

 to express satisfactorily the temperature influence on the velocity 

 of a number of chemical reactions, especially such which take place 



600 



cc. 



500 



400 



300 



and hour 



200 



too 



10 15 20 25 30 



FIG. 29. Temperature and metabolism of chrysalides. From " Bioch. Zeitschr." 



in dilute solutions. When the velocity of a reaction at a certain 

 temperature is v t it will, according to van't Hoffs rule, at a tempera- 

 ture 10 higher be z/ Mo = v t Q 10 where Q 10 is a constant 1 for the 

 reaction in question. For most of the chemical reactions studied 

 Q 10 lies between 2 and 3, that is the velocity is doubled or even trebled 

 when the temperature rises 10. 



When it is attempted to express the temperature variation of the 

 respiratory exchange by means of the rule of van't Hoff, Q 10 is found 



1 A slight decrease in Q 10 is regularly found for chemical reactions when the tempera- 

 tures are much increased, e.g. Q . 10 = 3-0, Q^^ = 2-3. The formula of Arrhenius 



Tf-To 



v t = v e q T * To in which q is a constant and T;, T the absolute temperatures (T t = 

 t + 273) generally expresses the facts observed in chemical experiments better than the 

 simple rule of van't Hoff. 



