VITALISM 19 



the presence of particles which are good for food causes the pro- 

 trusion of pseudopodia in a definite and purposive manner. 

 Probably the whole of at least the ectoplasm is to some extent 

 sensitive to stimuli of certain kinds, and it is also probable that 

 stimuli may be conducted from one part of the body to another 

 without the existence of special nervous tracts. 



One of the most difficult problems in connection with the 

 physiology of Amoeba and indeed of any living organism is 

 that of automatism. Does an Amoeba do anything really auto- 

 matically or spontaneously, or are all its actions the result, 

 direct or indirect, of the application of external stimuli to the 

 explosive molecules of living matter ? Is the organism merely a 

 machine run by the environment, or is it something more ? Here, 

 of course, at the very beginning of our investigations, we are face 

 to face with the old question, already referred to, of the existence 

 of an animating principle or " soul," which exercises some sort of 

 control over the physical and chemical processes upon which the life 

 of the organism depends. This is a question which perhaps falls 

 within the province of the philosopher rather than that of the 

 biologist. The theory of vitalism, by postulating the existence 

 of some such special vital force in all living things, undoubtedly 

 enables us to avoid many difficulties, but it is doubtful if it really 

 explains anything. As a matter of fact the more we study living 

 organisms by actual observation and experiment, the more 

 fully are we able to interpret their behaviour in terms of 

 chemistry and physics, but this is a very different thing from 

 saying that chemistry and physics will ultimately yield a 

 complete explanation of vital phenomena. 



It is quite possible, for example, that the movements of the 

 Amcebamay all ultimately be interpreted in such terms, for 

 Biitschli has shown that they can be closely imitated by minute 

 artificially prepared drops of oil-foam surrounded by water. The 

 substance of which these droplets are composed is of course 

 totally different chemically from protoplasm and is in no sense 

 alive, but it seems highly probable, if not certain, that since 

 purely physical processes (amongst which surface tension seems 

 to play an important part) are capable of producing strikingly 

 amoaboid movements in the oil-foam, they may also be largely, 

 if not solely, responsible for the similar phenomena of movement 

 in the living protoplasm of the Amoaba itself, which seems closely 

 to resemble an oil-foam in its physical properties. 



c 2 



