METABOLISM. 29 



warping actions, etc., but we cannot always draw 

 sharp lines between the various cases. Nor can we 

 directly measure the work done in the living 

 machinery ; but from the effects of pressures and 

 strains, the lifting of heavy weights, driving of 

 root-tips into soil, osmotic phenomena, etc., it is 

 certain that the values may be very high. 



The following classes of processes in living 

 protoplasm and cells may be taken as indicators. 

 First we have transformation of chemical energy,, 

 without which continued life is impossible : in 

 many cases e.g. the processes connected with 

 oxygen respiration these result in the develop- 

 ment of heat. Secondly, we have those remark- 

 able manifestations of energy known as osmotic 

 processes, which depend on surface actions, and 

 with which may be associated other surface effects,, 

 such as imbibition, secretion, etc,, and in con- 

 nection with which heat may be evolved or 

 absorbed. It is true the substances which exhibit 

 the properties here referred to may be produced, or 

 placed in position, by chemical energy, or they 

 may be absorbed by roots, etc. ; but the proximate 

 energy exhibited by them is not derived from 

 chemical energy, and may be out of all propor- 

 tion to the chemical energy of the substance or 

 substances concerned. Moreover it is significant 

 to note that a highly oxydised body may develop 

 much osmotic energy, as well as a highly com- 

 bustible one. 



It is of the greatest importance to realise the 

 truth that much work can be, and is done in 



