CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT 
HARVARD COLLEGE. NO. 264. 
THE OCCURRENCE AND THE SIGNIFICANCE OF 
PHOTOMECHANICAL CHANGES IN THE VERTE- 
“BRATE RETINA—AN HISTORICAL SURVEY 
LESLIE B. AREY 
Northwestern University Medical School 
FOUR FIGURES 
The exhaustive histological descriptions of the vertebrate 
retina published in the first half of the nineteenth century 
opened a field to physiological workers that has resulted in the 
production of many diverse investigations which, however, may 
be grouped into three general categories: 1) the physiology of 
the visual purple, 2) the action currents in the optic nerve, 
3) the changes produced in the retina chiefly through the action 
of light. Of these three divisions the effect of light upon the 
retina has proven to be especially interesting and instructive, 
yet, strangely enough, this field has hitherto remained almost 
the exclusive property of the workers of continental Europe. 
_ Stimulated by the results thus obtained among vertebrates, 
other investigators later undertook experimentation upon the 
invertebrate eye in order to discover whether similar con- 
ditions could be demonstrated among these animals. In the 
invertebrate types of eyes, however, due to the fundamental 
differences in structure, only partial agreement was to be expected. 
A review of the literature dealing with the changes produced 
in the visual cells and retinal pigment through the action of 
light has never been presented in English, although an excellent 
compilation was published in 1907 by the German writer Garten. 
Since, however, Garten’s review not only is of considerable 
length but also is inaccessible to many students, it has seemed 
desirable to present a brief summarization of the results that 
have been established by investigators in this field, together 
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