ANATOMY AND PHYSIOLOGY OF THE RETINA. 159 



head was covered for five minutes by a black cloth and then 

 exposed for three minutes to a somewhat clouded midday 

 sky. The head was then instantly decapitated, the eyeball 

 which had been exposed was rapidly extirpated by the aid of 

 yellow light, then opened, and instantly plunged in 5 per 

 cent, solution of alum. Two minutes after death the second 

 eyeball, without removal from the head, was subjected to 

 exactly the same processes as the first, viz. to a similar ex- 

 posure to the same object, then extirpation, &c. 



On the following morning the milk-white and now tough- 

 ened retinae of both eyes were carefully isolated, separated 

 from the optic nerve, and turned ; they then exhibited on a 

 beautiful rose-red ground a nearly square sharp image xoith 

 sharply defined edges ; the image in the first eye was some- 

 what roseate in hue and less sharply defined than that in the 

 second, which was perfectly white. The size of the images 

 was somewhat greater than one square millimetre. 



Professor Bunsen was amongst the witnesses of this beau- 

 tiful experiment. 



Arthur Gamgee. 



In a last communication to the ' Centralblatt,' No. 4, 27th 

 January, 1877, Professor Kiihne describes a very simple 

 method of optography, which from its singularity may be 

 used even for demonstration purposes. It is this. The head 

 of an ordinary rabbit kept in the dark after having been 

 severed is placed for ten minutes in such a position that one 

 eye is turned upwards, i.e. directed against one of the large 

 skylights of the laboratory, then the head is turned so that 

 the other eye may be exposed to the same influence. The 

 time of exposition was so long on account of the clouded 

 condition of the sky. After leaving them for twenty-four 

 hours in 5 per-cent. solution of alum, both eyes showed the 

 most marvellous images on the posterior surface at the 

 retina ; one recognises with great distinctness the outlines of 

 the skylight and the boards which were placed above the 

 glass as beautiful red stripes, and at some distance from them 

 there were seen even the top lights, the image of which could 

 not have been expected. The microscopic examination 

 showed complete integrity of the external segments of the 

 rods in the white parts of the images. 



