20 THE BEGINNINGS OF LIFE. 



the heat which is constantly operating upon it, and 

 'which is transformed into vital force by Its passage through 



the organised fabric 'which manifests it All the 



forces which are operating in producing the phenomena 

 of life are in the first place derived from the inor- 

 ganic universe, and are finally restored to it again. 

 .... And there is strong reason to believe that the 

 entire amount of force of all kinds received by an 

 animal during a given period is given back by it during 

 that period, his condition at the end of the time being 

 the same as at the beginning. And all that has been 

 expended in the building up of the organism is given 

 back by its decay after death.' 



In plants and in the lower tribes of animals we are 

 able to trace a most undoubted relationship between 

 the vital activity of each individual and the amount 

 of heat which it receives from external sources. Even 



bodies. Mr. Herbert Spencer says : ' We have next to note, as having 

 here a meaning for us, the chemical contrasts between those organisms 

 which carry on their functions by the help of external forces, and those 

 which carry on their functions by forces evolved from within. If 

 we compare animals and plants, we see that whereas plants, charac- 

 terised as a class by containing but little nitrogen, are dependent upon 

 the solar rays for their vital activities ; animals, the vital activities of 

 which are not thus dependent, mainly consist of nitrogenous substances. 

 There is one marked exception to this broad distinction, however ; and 

 this exception is specially instructive. Among plants there is a con. 

 siderable group the Fungi many members of which, if not all, can 

 live and grow in the dark ; and it is their peculiarity that they are very 

 much more nitrogenous than other plants.' (Principles of Biology, 1864, 

 vol. i. p. 37.) 



