152 PROFESSOR FRANZ BOLL. 



A Contribution to the Anatomy and Physiology of the 

 Ketina. By Professor Franz Boll, in Rome. (Trans- 

 lated from a paper communicated to the Royal Academy of 

 Science in Berlin, November 12, 1876 ; published in 

 *Monatsbericht der K. Akademie der Wissensch. zu Berlin/ 

 November 23rd, 1876.) 



The numerous histologists who, in continuation of the 

 well-known researches of Max Schultze, have lately examined 

 and described the rods and cones of the retina, which are 

 considered to be the terminal organs of the optic nerve, have 

 always believed that they had these interesting structures 

 before them in an " absolutely fresh " or " still-living " state. 

 But there can be no doubt that, up to the present time, not 

 one of all these observers has investigated a single retina of 

 any vertebrated animal in a true physiologically fresh condi- 

 tion, for they have all, without exception, missed the very 

 remarkable properties of the truly living retina, which will 

 be now described for the first time. 



If a frog which has been kept in the dark be decapitated 

 (the lower jaw is best left attached to the trunk), if an eye- 

 ball be then dissected out with the least possible loss of time, 

 cut in half with scissors, and the retina detached with fine 

 forceps from the dark ground of the retinal pigment and the 

 choroid, it appears at the first moment of an intense purple- 

 red colour, so that one might think a blood-clot had been taken 

 up by the forceps. During the next ten or, in favorable 

 cases, twenty seconds (stage 1), this colour gradually fades, 

 and after this time has usually disappeared altogether. The 

 retina then shows, during the next thirty to sixty seconds, 

 sometimes even longer (stage 2) a satiny lustre. Gra- 

 dually this also becomes lost, and the retina becomes perfectly 

 transparent, in which state it remains for a quarter of an 

 hour or more (stage 3). Then it gradually becomes turbid 

 and opaque (stage 4), 



Concerning the causes of these hitherto unknown optical 

 properties of the physiologically fresh retina, microscopic 

 examination shows that both the purple colour of the first 

 stage and the satiny lustre of the second are seated ex- 

 clusively in the layer of rods, or rather in their strongly 

 refracting external segments, which are composed of ex- 

 tremely delicate superimposed plates ; these appear purple- 

 red in the first stage, and shine like satin in the second. 

 Towards the end of the second stage the rods swell up and 



