FACTS 



163 



whenever the dose of malic acid was properly arranged, by 

 being drawn into the capillary tube. 



Such a capillary tube became a real trap for fern anthero- 

 zoids. 



This was an elegant way of showing the influence of malic 

 acid on the movements of fern antherozoids. By repeating 

 the same experiment with all the chemical products whose 

 heterogeneous distribution through the liquid might influence 

 the antherozoids' movements, and by analogous experiments 

 which are easy and have been done with various physical 

 agents (light and heat radiations and the like), the very com- 

 plex movement of antherozoids can be decomposed into all 

 its elements. In other words, the irritability peculiar to this 

 cell species can be thus reduced to a sum of perfectly well 

 defined tactisms. 



After this nothing remains of the pretended spontaneity 

 of movement in living bodies. An observer conversant 

 with the results of all these experiments in tactisms knows 

 that the movements he observes in living bodies through the 

 microscope are due to the colloid and chemical reactions of 

 the mobile beings and the medium. 



Nevertheless, it is impossible to know every instant the 

 heterogeneous conditions realized in the drop of water and, 

 consequently, it will be impossible for the observer to 

 foresee at any given moment the movements which the 

 infusoria are going to perform. And so, if he pleases, he 

 may keep to the old manner of describing vital phenomena 

 and say that infusoria move as they please, for reasons that 

 remain unknown. 



