STUDIES IN SPECIAL SENSE PHYSIOLOGY 



BY M. GREENWOOD, JUNR. 



PAKT I. VISUAL ADAPTATION 



IF one asked a number of students, taken at random, which de- 

 partment of physiology seemed to them the least interesting, I 

 am confident that a majority would award the palm of dulness 

 to that subdivision which treats of the special sense mechanisms. 



It is, indeed, not difficult to understand such a result. Our 

 knowledge of special sense physiology is at once very complete and 

 very incomplete ; observations and experiments have accumulated 

 to an enormous extent, yet we are far from the synthesis of these 

 results which makes the inter-relationship of the various parts 

 clear and enables the intelligent reader to perceive that the sub- 

 ject is an harmonious system, not a mere collection of disconnected 

 fragments. 



I think, therefore, the reader will more easily appreciate the 

 scope and method of this branch of science if I choose two 

 problems only, and examine them in detail, not so much because 

 they are of practical importance, but as illustrations of the lines 

 upon which modern thought and experimental work seem to 

 advance. 



Ill the present section, I shall sketch the course of recent in- 

 quiries into the phenomena of adaptation of the eye to various 

 intensities of light, a subject which illustrates the practical methods 

 of work ; in the later section I shall attempt to set out the principles 

 of two modern theories of colour vision, and to show how far they 

 may be regarded as really new contributions to science, and to 

 what extent they are products of thought handed down to us from 

 remote ages. Here, as in so much of modern science, we shall 

 find that old and new are inextricably interwoven, that much of 

 what is taken to be modern is so only in a geological sense. 



It has long been known that the nature of the response by the 



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