45 
ical reaction, which accompanies the diffusion process. Hence it 
is useless to try and determine the order of a heterogeneous 
reaction, from the velocity with which it proceeds. 
d. The temperature coefficients of heterogeneous reactions are 
small, (viz, about 1.2 for a 10° rise). 
In this connection it is interesting to note that photo-chemical 
reactions have small temperature coefficients (viz. about 1.1 for a 
10° rise). | 
Now I shall diseuss the results obtained in physiological proces- 
ses with regard to the influence of temperature on them. 
The relation between the temperature and the velocity of respir- 
ation has been studied during the last few years both for plants 
and animals. The principal object of these investigations has been 
to find out whether respiration can be considered as a chemical 
process. 
From the researches of CLAUSEN (Landwirt. Jahrbuch Bd. 19 1890), 
BrLACKMAN (Annals of Botany 1905, 19, 288), Kuprr (Rec. Trav. 
Bot. Néerl. 1910, 7, 181) LrHeNBAUER (Physilogical researches N°. 5, 
Avausr 1914), Miss Lerrscn (Annals of Botany January 1916), Miss 
SAUNDERS (private communication) and others we find that the 
temperature coefficients of plant processes generally lie between 2 
and 3 for a 10° rise of temperature. 
Brown and Worry (Proc. Roy. Soc. 1912, 85 B, 546) have 
shown that the temperature coefficient of the velocity of absorption 
of water by different seeds is about 2 for a 10° rise. If the values 
of the velocity coefficients are calculated from their results, we see 
that they follow the unimolecular formula. 
The researches of Vetny and Water (Proc. Roy. Soc. 1910, 
82 B) show that the ArrHeENius formula can be applied to the 
influence of temperature on the velocity of the action of drugs on 
muscles. 
Very large number of experiments have been made on the 
influence of temperature upon metabolism both in cold-blooded and 
in warm-blooded animals. But comparatively few of them have been 
made under standard conditions. In most cases animals have been 
free to move about and even in cases where they have been tied, 
muscular movements have not been prevented or muscular tone 
abolished. In these conditions a fundamental difference has been 
observed between the effects of temperature upon cold-blooded and 
upon warm-blooded animals. In cold blooded-animals the respiratory 
exchange almost always rises with increasing temperature, but 
generally irregularly and toa very different degree in different animals. 
