2 THE BIOLOGY OF DAILY LIFE. 



bj fitted in time, direction, and amount to meet the 

 action B a change which is often required to be much 

 larger than its antecedent. 



" Mark, now, the relation between these two final 

 results. On the one hand, for the maintenance of 

 that correspondence between inner and outer actions 

 which constitutes Life, an organism must be susceptible 

 to small changes from small external forces (as in 

 sensation), and must be able to initiate large changes 

 in opposition to large external forces (as in muscular 

 action). On the other hand, organic matter is at 

 once extremely sensitive to disturbing agencies of all 

 kinds, and is capable of suddenly evolving motion in 

 great amounts. That is to say, the constitution of 

 organic matter specially adapts it to receive and pro- 

 duce the internal changes required to balance external 

 changes. 



"This being the general character of the vital 

 Functions, and of the Matter in which they are 

 performed, the science of Biology becomes an account 

 of all the phenomena attendant on the performance 

 of such Functions by such Matter an account of all 

 the conditions, concomitants, and consequences, under 

 the various circumstances fallen into by living bodies." 

 (Principles of Biology, vol. i., pp. 94 and 95.) 



