110 THE PHILOSOPHY OF BIOLOGY 



is valid ; that we are justified in seeing physico-chemical 

 activities in life. But are these results all that we have 

 reason to expect ? 



We turn now to Bergson's fertile comparison of 

 the physiological analysis of the organism with the 

 action of a cinematograph. If we take a series of 

 photographic snapshots of, e.g., a trotting horse and 

 then superpose these pictures upon each other, we 

 produce all the semblance of the co-ordinated motions 

 of the limbs of the animal. Yet all that is contained 

 in the simulated motion is immobility. From a suc- 

 cession of static conditions we appear to produce a 

 flux. Yet if we could contract our duration of, e.g., 

 a week, into that corresponding to five minutes — if 

 we could speed up our perceptual activity — should 

 we not see the cinematographic pictures as they really 

 are — a series of immovable postures and nothing more : 

 truly an illusion ? If, again, we reverse the direction 

 of motion of the film, we integrate our snapshots 

 into something which is absolutely different from the 

 reality which they at first represented ; and by such 

 devices the illusions and paradoxical effects of the 

 picture-house farces are made possible. Well, then, 

 in the physiological analysis of the activity of the 

 organism do we not do something very analogous to 

 this ? The complexity of even the simplest function 

 of the animal is such that we can only attend to one 

 or two aspects of it at once, arbitrarily neglecting all 

 the rest. We find that the hydrostatic pressure of 

 blood, and lymph, and secretion, the osmotic pressure, 

 the diffusibility, vaso-motor actions, and other things 

 must be investigated when considering the question 

 of how the submaxillary gland secretes saliva. One, 

 or as many as possible, of these reactions are in- 

 vestigated at one time, and then the results are pieced 



