Bauhaus-Universität Weimar

Helmholtz's treatise on physiological optics. Volume 2. Edited by James P. C. Southall. Translated from the 3rd German edition
Helmholtz, Hermann von
The Sensations of Vision 
[376. K. 
tion and are connected with the formation of visual purple; in other 
words, they have an external basis in the sense that they are not 
directly dependent on the sensation process.—Among hypotheses 
connected with Hering’s fundamental ideas, the proposals made by 
Pauli1 and by Brunner2 may be referred to. They are likewise 
concerned with the nature of the processes underlying sensations, 
especially with the mode of antagonism that has to be hypothecated 
between processes combined in one pair. With respect to the anomalies 
of colour vision, these theories certainly need to be amplified exactly 
in the same way as the original theory of opponent colours; and, 
according to what has been stated already, this amplification would 
have to do with the external part of the organ of vision. As to the 
basis of sensation itself, the writer thinks that the proposals made by 
Pauli and Brunner amount to far more considerable changes in 
Hering’s theory than they themselves realize; changes which enable 
the theory to get rid of many difficulties, but also involve it again in 
many others. The interest of the entire conceptions, and especially the 
way in which they differ from the original theory, is connected chiefly 
with general biological questions; and therefore a thorough discussion 
has to be omitted here and reserved for another occasion. 
An idea that is apparently at the basis of many of these attempted 
explanations was first expressed by Donders. He supposed that the 
sensations are associated throughout by cleavage-processes. The col¬ 
ourless sensations are due to total cleavages (symmetrical or un- 
symmetrical) of highly complex molecules, whereas the coloured 
sensations are due to partial cleavages. Schenck’s theory mentioned 
above and Ladd-Franklin’s theory, which is very similar to it, are 
closely related to this idea. 
On the other hand, Bernstein3 has developed a theory of visual 
sensations on an entirely different basis. This theory makes use of 
special conceptions concerning the processes in the central nervous 
system, including inhibitory effects. 
The very diversity of the results of all these speculations, in spite 
of the fact that they all staçt from very similar premises, merely 
serves to show what wide room there is here for hypotheses. The 
writer has expressed the opinion over and over again that it is idle at 
present to tackle these questions; and recent experiments (especially 
one of Schenck’s) tend to confirm this opinion. Of course, it is a 
matter of individual scientific disposition and personal taste as to 
how far one can go in this direction. 
1 Pauli. Der kolloidale Zustand und die Vorgänge in der lebendigen Substanz. 1902. 
2 Pflügers Archiv CXXI. S. 370. 1908. 
3 Naturwissenschaftliche Rundschau: XXI. S. 497. 1906.


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