rrf ftaiural Jpbtorjr Sdentes. 



Our conclusions on the first of these heads must 

 depend, of course, upon the nature of the subject- 

 matter of Biology ; and I think a few preliminary 

 considerations will place before you in a clear light 

 the vast difference which exists between the living 

 bodies with which Physiological science is concerned, and 

 the remainder of the universe ; between the phsenomena 

 of Number and Space, of Physical and of Chemical force, 

 on the one hand, and those of Life on the other. 



The mathematician', the physicist, and the chemist 

 contemplate things in a condition of rest ; they look 

 upon a state of equilibrium as that to which all bodies 

 normally tend. 



The mathematician does not suppose that a quantity 

 will alter, or that a given point in space will change 

 its direction with regard to another point, sponta- 

 neously. And it is the same with the physicist. When 

 Newton saw the apple fall, he concluded at once that 

 the act of falling was not the result of any power 

 inherent in the apple, but that it was the result of the 

 action of something else on the apple. In a similar 

 manner, all physical force is regarded as the disturbance 

 of an equilibrium to which things tended before its 

 exertion, to which they will tend again after its 

 cessation. 



The chemist equally regards chemical change in a 

 body, as the effect of the action of something external 

 to the body changed. A chemical compound once formed 

 would persist for ever, if no alteration took place in 

 surrounding conditions. 



But to the student of Life the aspect of Nature is 

 reversed. Here, incessant, and, so far as we know, 

 spontaneous change is the rule, rest the exception 

 the anomaly to be accounted for. Living things have 

 no inertia, and tend to no equilibrium, 



