GENERAL INTRODUCTION 5 



individual processes, and then study each process, or 

 group of processes, by itself (if this be at all possible) and 

 to determine also the relations between various processes. 

 The number of separate processes, distinguishable to the 

 scientist, is practically unlimited, owing to the fact that 

 we can subdivide, again and again, and consider as a 

 separate process each detail of a chemical reaction, as 

 well as the diffusion of each compound from one cell to 

 another. For scientific study, we divide life manifesta- 

 tions into groups which are logically comparable, and 

 which fulfil the same purpose. Such groups of processes, 

 we call functions, or more correctly partial functions, 

 since each of them is only part of the complete life proc- 

 ess. The eating of meat by a cat and the eating of grass 

 by a cow are such separate processes, classified under 

 the same function; while the running of a horse, the 

 flying of a bird, and the swimming of a bacterium give 

 us an idea of the variability of the function which we 

 ordinarily call motility. 



The distinction of functions is primarily a matter of 

 convenience or viewpoint, and this varies with one's 

 personal attitude, as well as with the progress of knowl- 

 edge. The viewpoint of Pasteur that fermentation and 

 respiration were but two modifications of the same 

 function has been contested most persistently for a long 

 time. Further, it must be stated that we distinguish 

 more functions, ordinarily, in the higher organisms; in 

 other words, what is only one function in the protozoon, 

 may be divided into four or five functions in man. The 

 terms function and partial function relate, therefore, 

 not to well defined groups of processes; and they cannot 

 be well defined, because they are interlinked in such a 

 way that some of the processes are necessary prerequisites 

 for the others, — e.g., respiration is the prerequisite for 



