ANATOMY AND PHYSIOLOGY OF THE RETINA. 155 



result from anatomical discovery above mentioned, and which 

 may be now at least shortly referred to : 



.1. The red colour of the back of the eye as seen by the 

 ophthalmoscope does not depend upon illumination of the 

 blood-vessels of the choroid, but arises essentially from the 

 purple colour peculiar to the retina. 



2. This special colour of the retina is only present during 

 life, and survives the death of the animal (especially in warm- 

 blooded animals) only a few seconds. If a dying animal be 

 examined with the ophthalmoscope (it is best to kill it with 

 chloroform) the moment of death is marked by a sudden 

 paling of the red fundus oculi ; on this fact an easily appli- 

 cable method of determining death may be without difficulty 

 founded for forensic purposes. 



3. The special colour of the retina is considerably dimi- 

 nished intra vitam by incident light. Diffused daylight 

 makes the purple colour of the retina pale. Long action 

 of direct sunlight (dazzling) completely decolorises the 

 retina. In the dark the intense purple colour is immediately 

 restored.^ 



This objective alteration of the outer segments of the rods 

 by rays of light undoubtedly forms a part of the act of 

 vision. 



We append here a communication by Professor Arthur 

 Gamgee to * Nature,' February 1st, 1877, . on Professor 

 Kiihne's recent observations induced by Boll's discovery. 



Professor Kiihne read before the Naturhistorisch-Medicin- 

 ischer Verein of Heidelberg, on January) 5th, 1877, a paper 

 entitled ' Zur Photo-chemie der Netzhant,' in which, while 

 confirming the fundamental statement of Boll, he has recorded 

 a number of new facts of great interest. 



Kuhne*s Researches on Photo-chemical Processes in the 

 Retina. 



On January 5th, Dr. W. Kiihne, Professor of Physiology 

 in the University of Heidelberg, read before the Naturhis- 

 torisch-Medicinisches Verein, of Heidelberg, a paper entitled 

 " Zur Photo-chemie der Netzhaut/' so full of interest to the 



' These facts were not yet known to me when, in June of the present 

 year, I demonstrated the red retina of the frog at Berlin to MM. du Bois- 

 B.eyraond, Helmholtz and Pringsheim. The frogs used for the purpose had 

 been kept in a rather light room, and my demonstration only succeeded 

 after about half a dozen frogs had been sacrificed in vain. If care has 

 been taken to keep the frogs in the dark, the demonstration, with a little 

 skill, succeeds without fail in the first eye. 



VOL. XVII. NEW SER. L 



