98 PROCEEDINGS OF THE SOCIETV. 



received by this eye was quite satisfactory, and in fact was rather an 

 advantage. 



Dr. Shillington Scales said he wished to convey his sincere thanks to 

 Dr. Jentzsch for his paper, and to Mr. Ogilvy for having brought it 

 forward, and he quite agreed with Mr. Beck and Mr. Cheshire in think- 

 ing it probably marked a new departure. Many drawbacks which had 

 hitherto been attached to binocular Microscopes would also seem to have 

 been met. There was one part of the paper, however, which he could 

 not quite follow. While all were agreed on the great advantage of 

 using two eyes instead of one in microscopical work, he failed to see 

 what bearing the discussion had in regard to the respective parts played 

 by rods and cones as affected by comparative darkness and light. Von 

 Kries' theory is that the function of the cones is to give us vision of the 

 chromatic and achromatic order in daylight, and that of the rods and 

 visual purple vision of the achromatic order in twilight or after rest in 

 the dark. As daylight failed the rods came into play, giving us achro- 

 matic vision, but he did not see how this theory bore upon the advantage 

 of binocular vision, except in a very general way. In regard to the 

 question raised by Mr. Blood, as to seeing certain colours better than 

 others, he wondered whether recent work in connexion with sensitivity 

 to various colours might shed any light upon this subject. As light 

 failed or was reduced, the blue-green part of the spectrum took ou ar 

 increased comparative sensibility and showed itself on the retina. This 

 applied to the periphery rather than the fovea cerebralis. Whether this 

 had any bearing on the subject he did not know. Personally, he used 

 the very least amount of light possible, as, apart from the care of the 

 eyes, he considered more could be seen by reducing the amount of light 

 (he was not here referring to the use of the diaphragm), especially 

 when dealing with stained preparations. This was one of several 

 physiological questions raised by Dr. Jentzsch's paper. 



Mr. Barnard agreed with what had been said in regard to the 

 advantage of the binocular Microscope over the monocular. He was 

 in the habit of doing biological work, and, unlike those mentioned by 

 Dr. Jentzsch who would not use both eyes alternately in monocular 

 work, he did do this, but there was no doubt that the fatigue experienced 

 by the unused eye did in a short time spread itself over both eyes. With 

 a binocular instrument, however, he felt that he could work for an 

 almost indefinite time with a light of moderate intensity. There was, 

 of course, the question raised by Mr. Blood in regard to the difference 

 in sensitiveness to colour of the two eyes, which he had himself ex- 

 perienced lately in an interesting manner when working with the 

 ultra-violet Microscope. Here he experienced considerable difficulty in 

 focusing with the right eye, but the difficulty was less when using 

 the left. 



The only practical objection which had been raised in regard to 

 Mr. Beck's instrument was that referred to by Mr. Blood. The altera- 

 tion in tube which occurred as the result of adjustment for intra-ocular 

 distance was a point for consideration, and might in extreme cases be a 

 real objection to the particular method adapted. 



Mr. Beck, in reply to Mr. Rheinberg's remarks on stereoscopic 



