10 ZOOLOGY. 



material for plant-life. We have good reason to believe 

 that, in spite of the enormous mutual destruction of living 

 things, the actual quantity of living matter on the earth's 

 surface is still increasing, on the whole, as we know it has 

 steadily done for ages past. Thus there has been a gradual 

 drain of material from the dead crust of the earth into the 

 substance of living creatures, first into plants, and then 

 through both plants and animals. But to build up from 

 the simple compounds of the earth's crust, or from those 

 excreted by animals, the complex compounds of plants, a 

 constant inflow of energy is needed, and this is supplied by 

 the radiant energy that comes to us from the sun. 



16. Metabolism in Plant and Animal. Such is the 

 general view which modern science takes of the relation of 

 the animal and plant kingdoms to one another, and to the 

 inorganic world. To express this relation briefly and clearly 

 we need two or three terms of modern introduction. The 

 whole of the chemical changes which go on in every living 

 organism are collectively termed metabolism. They may be 

 grouped under two heads. Firstly we have synthetic 

 processes, by which simple compounds are built up into 

 complex ones, energy being absorbed and stored up in these 

 complex compounds : these collectively constitute anabolism. 

 Secondly, there are the processes by which the highly 

 complex living matter built up by anabolism undergoes 

 decomposition and oxidation, with transfer of energy 

 and the performance of physical work: these constitute 

 katabolism : the comparatively simple, oxidized compounds 

 resulting are called katastases. 



Evidently the essential difference between plant and 

 animal is that the plant is, on the whole, passive and 

 anabolic, the animal active and katdbolic. Not that the 

 metabolism in either case is exclusively of the one kind, but 

 that there is a balance in the one or the other direction. 



17. Morphology and Physiology. In our study of the 

 rabbit, and of all our other types, we shall constantly 

 have to look at things from two different points of view 

 that of structure and that of function. From the former 



