98 RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



to vary greatly, and in the experiments which have given the most 

 uniform results Q 10 shows a steady and very large decrease with in- 

 creasing temperature. For the curves shown in figs. 28 and 29 we 

 have : 



TABLE XVII. 



When an actual temperature-metabolism curve is compared with a 

 van't Hoff curve constructed from the " average Q 10 ," it is seen that at 

 low temperatures the observed increase in metabolism by increasing 

 temperature is larger than the theory would demand, while at high 

 temperatures it is smaller. Fig. 30 shows such a comparison. Q 10 = 

 3-9 is the average of all the observed values for Q 10 . In Q 10 =274 

 the highest value for o to 5 has been arbitrarily excluded. 



It is to the writer's mind not very probable a priori that the re- 

 spiratory exchange of any animal should follow the rule of van't Hoff, 

 since we have to do not with a single chemical reaction taking place 

 in a dilute solution, but with a very complex series of reactions 1 

 which perhaps cannot even be regarded as taking place in a homogene- 

 ous medium or between substances in dilute solution. If, however, the 

 differences between the conditions in the cells and those in homogeneous 

 dilute solutions should be negligible, and if further all the reactions in- 

 volved should be influenced by the temperature in accordance with the 

 rule of van't Hoff, the result must nevertheless show a considerable 

 divergence if a limiting factor comes into play. Reasons have been 

 given above for assuming that the oxygen pressure in the tissues is 

 probably in many cases a limiting factor for the oxidative phase of the 



1 Several inorganic complex reactions have been observed in which the rule of van't 

 Hoff does not hold, and one has been found in which the reaction velocity decreases with in- 

 creasing temperature (Miss Benson, " Journ. of Phys. Chem.," 1904, 8, 116). A critical 

 summary of the applicability of the rule of van't Hoff both to chemical and to a number of 

 physiological processes has been given by Jeanne van Amstel, " De Temperatursinvloed 

 op physiologische processen der alcoholgist ". Proefschrift, Amsterdam, 1912 (Dutch). 



