CHAPTER I. 
Contemplations on Chemotaxis. 
$ 1. The chemotactical phenomena caused by stimulation. 
The occasion to this investigation was a study of 
literature and some provisional experiments on chemotaxis. 
As a rule, people are of opinion, that chemotactic 
phenomena appear, when a substance that works attractive 
or repulsive, forms zones of diffusion. 
Swimming on the organism continually comes in another 
medium, as the chemotacticum is not always present in 
the same concentration. It reacts upon this change of 
concentration and alters its direction of movement. 
We must accept that the chemotacticum affects elements 
of the cell, either local or as a whole. Perhaps by this 
affection, perhaps by changes which closely depend on 
it, a stimulation is called forth, the consequence of which 
is that the motion is changed. 
The real stimulation process is considered to exist in 
the taking up of the stimulus (the perception), the con- 
ducting of the stimulus and after that unknown actions 
which lead to the reaction. The reaction is the criterium 
by which we judge the chemotaxis. We must pay attention 
to the appearance of the reaction, as well as to its intensity. 
That concentration of the chemotacticum which is able 
