ical reaction, whicb accompanies the difFosion process. Hence it 
is useless to try and determine the order of a heterogeneous 
reaction, from the velocit}' with which it proceeds. 
cl. 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 srnall temperature coefticients (viz. about 1.1 for a 
10° rise). 
Now I shall discuss the resulls 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 jears both for plants 
and animals. The principal object of these investigations has been 
to find out whetlier respiration can be considered as a Chemical 
process. 
From the researches of Clausen (Ijandwirt. Jahrbuch Bd. 19 1890), 
Blackman (Annals of Botany 1905, 19 , 288), Kuijper (Ree. Trav. 
Bot. Néeri. 1910, 7 , 131) Lehenbaüer (Physilogical researches N®. 5, 
August 19J4), Miss Leitsch (Annals of Botany January 1916), Miss 
Saunders (private communication) and others we ünd that the 
temperature coefficients of plant processes generally lie between 2 
and 3 for a 10° rise of temperature. 
Brown and Worley (Proc. Roy. Soc. 1912, 85 B, 546) have 
shown that the temperature coëfficiënt 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 Veley and Waller (Proc. Roy. Soc. 1910, 
82 B) show that the Arkhenius formula can be applied to the 
influence of temperature on the velocity of the aelion of drugs on 
muscles. 
Very large number of experiments have been made on the 
influence of temperature upon metabolisrn both in cold-blooded and 
in warm-blooded animals. But comparativelv 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 to a very different degree in different animals. 
6 * 
