Incipient Vitality. 29 
however, is not what one expects or finds in the plant at tem¬ 
peratures of which it has had previous experience. How then is 
regulation attained ? This is the first step to be considered in 
building up a synthetic conception of cell-activity from the known 
activity of its isolated enzymes. 
The biological study of chemical reactions by the physical 
chemist has shown that temperature and mass are the two primary 
factors that control the rate of reactions in the test-tube. All 
reactions are accelerated by a higher temperature, and the accel¬ 
eration is generally approximately uniform. For the sort of 
reactions that take place in the cell, the rapidity of the change is 
doubled or trebled for each rise of 10"C. Now we find in the 
higher animals that the temperature of the body is very carefully 
kept at a uniform level, which is much above that of the environ¬ 
ment. Of course the heat needed has to be generated by certain 
special metabolic changes, but there is a uniform high rate of 
general metabolism attained in this way, and the system is thus free 
to adjust itself to various other calls upon it. The higher plants 
are very different from this, and are entirely subject to external 
temperatures. They must therefore survive wide ranges of tem¬ 
perature variation naturally, and they can resist still wider ranges 
experimentally. There is no evidence that they seek to com¬ 
pensate the direct physico-chemical effects of temperature changes 
by regulatory process, but the plant has hardly been investigated 
critically from this point of view. It is true that a leaf in direct 
sunshine cools itself by the evaporation of water, but this seems 
to be of secondary significance. 
One must not think that plant-cells are fundamentally so 
sluggish that the higher activity conditioned by a high body- 
temperature is impossible for them. Does not the Arum spadix 
raise its temperature up to even 50°C, and some 34 n C above its 
environment by the local activity of its metabolism ? Does not 
the stalk of the sporogonium in Pellia grow from a length of 
two millimetres to eighty millimetres in three or four days ? Yet 
the plant submits to have its metabolism varied with every passing 
change of external temperature. Nevertheless it distinguishes 
itself from the inert masses around it by regulation of its 
metabolism, for such is the essential of life, but not by regulation 
by means of temperature. 
A consideration of other methods of regulation brings us to 
some discussion of the influence of mass on the rate of chemical 
