CHAPTER II 



THE FUNCTIONS OF THE ORGANISM 



ADOPTING, as our point of departure, the con- 

 ception of an organism as a machine adapted to 

 the performance of certain duties or functions, let 

 us, first of all, inquire what, speaking generally, these 

 functions are ? What are the essential kinds of work 

 that all organisms carry out ? A little reflection will 

 lead us to the conclusion that every living organism 

 Functions exhibits three fundamental capacities, viz., (1) The 

 organism ca P ac ity f r feeding itself ; (2) the capacity for 

 responding to stimuli to impulses from within or 

 from without ; (3) the capacity for multiplying 

 itself ; in other words, the three fundamental physio- 

 logical characteristics of the organism are nutrition, 

 sensitivity, and reproduction. Further, just as a 

 butcher's knife, a cavalry sabre, an anatomist's 

 scalpel, a surgeon's lancet, are all of them knives, 

 and all alike fulfil the general purpose of making an 

 incision, although each is constructed in the way 

 best suited to produce the special kind of incision 

 intended, so organisms show the greatest variety in 

 constructive detail, in all cases adapted to carry out 

 these functions in very varied ways. Let us, quite 

 briefly, summarise what we understand these three 

 general functions to consist in. 



Every organism must obviously be able to absorb 



from without certain materials which, however 



Nutrition, complex they may be in chemical composition, 



are still not themselves alive. These materials, 



