2 INTRODUCTORY. 



And lience biology is more precisely defined as the science which 

 treats of matter in the living state. 



The Relationship between Living and Lifeless Matter. Al- 

 though living matter and lifeless matter present this remarkable 

 contrast to one another, they are most intimately related, as a 

 moment's reflection will show. The living substance of the human 

 body, or of any animal or plant, is only the transformed lifeless 

 matter of the food which has been taken into the body and has 

 there assumed, for a time, the living state. Lifeless matter in 

 the shape of food is continually streaming into all living things 

 on the one hand and passing out again as waste on the other. 

 In its journey through the organism some of this matter enters 

 into the living state and lingers for a time as part of the body 

 substance. But sooner or later it dies, and is then for the most 

 part cast out of the body (though a part may be retained within 

 it, either as an accumulation of waste material, or to serve some 

 useful purpose). Matter may thus pass from the lifeless into the 

 living state and back again to the lifeless, over and over in never- 

 ending cycles. A living plant or animal is like a fountain or a 



flame into which, and out of which, matter is constantlv stream- 



ti 



ing, while the fountain or the flame maintains its characteristic 

 form and individuality. It is 4 ' nothing but the constant form of 

 a similar turmoil of material molecules, which are constantly 

 flowing into the organism on the one side and streaming out on 

 the other. . . . It is a sort of focus to which certain material par- 

 ticles converge, in which they move for a time, and from which 

 they are afterward expelled in new combinations. The parallel 

 between a whirlpool in a stream and a living being, which has 

 often been drawn, is as just as it is striking. The whirlpool is 

 permanent, but the particles of water which constitute it are in- 

 cessantly changing. Those which enter it on the one side are 

 whirled around and temporarily constitute a part of its indi- 

 viduality ; and as they leave it on the other side, their places are 

 made good by newcomers.' (Huxley.) 



How then is living matter different from lifeless matter ? 

 The question cannot be fully answered by chemical analysis, for 

 the reason that this process necessarily kills living matter, and 

 the results therefore teach us little of the chemical conditions ex- 

 isting in the matter when alive. Analyses, nevertheless, bring 



