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the cutilar products of the lamellas is the intermediate factor of the 
movements of the air in the lungs. 
I must however still add that in special circumstances some 
more important movements of inhalation and exhalation can be 
observed, which are brought about by the operations of muscles of 
the body and of a special muscle of the vestibulum. I intend to 
discuss these in a subsequent communication. 
Physiology. — “On the nature and progress of visual fatigue”. 
By Dr. A. A. GRÜNBAUM (Odessa). (Communicated by Prof. 
G. vaN RIJNBERK) '). 
(Communicated in the meeting of May 27, 1916). 
The problem of visual fatigue has, in contrast with cognate 
problems as those of light- and darkness-adaptation hardly been 
broached from an experimental side. 
The widely spread, purely theoretical views have from one side 
contributed to this fact, according to which the self-regulation of 
optically sensitive substances leads to a practical indefatigability. 
(HeriNg). On the other hand the traditional postulate, according 
to which the application of very strong optical stimuli in itself lies 
already beyond the physiologic limits of the pathological domain, 
plays an important part in the neglect of our problem. 
Notwithstanding this I have only been conducted by purely 
experimental requirements and consequently selected strong stimuli, 
causing a positive fatigue. A 400 N. K.-lamp e.g., tempered by a 
milk-glass and placed at a distance of 1.25 m. from the experi- 
mental person, forms such a stimulus. 
I have studied the progress of the fatigue caused by this light-stimulus 
by availing myself of the already often investigated phenomena of 
flickering’. 
When we cause a light-stimulus to influence, intermittingly with 
a dark pause, on the eye, we can at a definite frequency of the 
succeeding stimuli no longer distinguish them; the impressions fuse, 
and from the flickering light the impression of a relatively quiet 
light is experienced. 
The number of light stimuli (and consequently likewise that of 
1) The results recorded here form part of a series of experiments made in the 
years 1914—16 in the Physiological Laboratory of the University of Amsterdam, 
serving to obtain the venia legendi in experimental psychology at the Medical 
Faculty there. 
