NEUROBIOTAXIS 265 
Then I found—though not starting my work with a psychologi- 
cal secope—that the anatomical relations of the dendrites and the 
cells in the nervous system were regulated in accordance with the 
law which, in psychology, is known as the law of association, 
in which law (in all the different forms’ in which it may appear) 
the simultaneity of stimulations or residua of stimulations is 
the essential part. 
Fig. 2. Tetrodon, showing the ventral position of the abducens nucleus. 
f.l.p., fasciculus longitudinalis posterior; Nuc.VI, abducens nucleus; N.VJ, 
abducens nerve; r.V/7,m., motor facialis root; tr.t.b.v., tractus tecto-bulbaris 
ventralis. After Van der Horst. 
This anatomical observation, first made on motor cells, led 
me to study more carefully the courses of several axon-tracts, 
sensory tracts, as well as the so-called ‘‘central motor tracts,” 
such as the pyramids, and it soon appeared to me that a criti- 
8 Those forms are simultaneity, successivity, similarity and contrast. In the 
three first named forms the presence of one stimulus, or remains of a stimulus, 
while the other is added, is obvious. The association by contrast is also due in 
the first place to simultaneity of impression since the simultaneous or successive 
contrast makes us discriminate things: black and white, father and mother, etc. 
