140 



Messrs. Frankland and Duppa on the 



[Feb. 18, 



13. The orderly arrangement of the several layers and their elementary 

 parts is maintained by a frame of connective tissue which consists of — 



I, an unbroken homogeneous membrane bounding the inner surface of the 

 retina, the membrana limitans interna ; 2, a fenestrated membrane which 

 holds the rods and cone-bodies, the membrana limitans externa, first 

 correctly described by Schultze ; 3, an intermediate system of tie-fibres — 

 Miiller's radial fibres — connected with which in the layer of inner granules 

 are certain oblong and fusiform bodies of uncertain nature ; 4, the inter- 

 granular layer; 5, an areolated tissue, open in the layers of outer and 

 inner granules, and very closely woven in the granular layer. 



14. No blood-vessels occur in the reptiUan retina. 



II. Notes of Researches on the Acids of the Lactic Series. — No. I. Ac- 

 tion of Zinc upon a mixture of the Iodide and Oxalate of Methyl." 

 By E. Frankland, F.R.S., Professor of Chemistry, Royal Insti- 

 tution, and B. F. Duppa, Esq. Received February 10, 1864. 



In a former communication by one of us*, a process was described by 

 which leucic acid was obtained synthetically by the substitution of one 

 atom of oxygen in oxalic acid by two atoms of ethyl. 



The relations of these acids to each other will be seen from the following 

 formulsef : — 



^ 'an. 



OH ^ 



OH 



OH 

 OH 



Oxalic acid. Leucic acid. 



This substitution of ethyl for oxygen was effected by acting upon oxalic 

 ether with zincethyl. On distilling the product with water, leucic ether 

 came over, which on treatment with an alkali yielded a salt of leucic acid. 



We have since found that this process may be much simplified by gene- 

 rating the zincethyl during the reaction, which is effected by heating a 

 mixture of amalgamated zinc, iodide of ethyl, and oxalic ether in equivalent 

 proportions to the necessary temperature. 



The operation may be considered complete when the mixture has soli- 

 dified to a resinous-looking mass. This, treated with water as in the for- 

 mer reaction and distilled, produces quantities of leucic ether considerably 

 greater than can be obtained from the same materials by the first mode of 

 operating. Thus the necessity for the production of zincethyl is entirely 

 obviated, the whole operation proceeds at the ordinary atmospheric pressure, 

 and a larger product is obtained. 



"We find that this process is also applicable to the homologous reactions 

 with the oxalates and iodides of methyl and amyl. By it we have obtained 



* Proceedings of the Royal Society, vol. xii. p. 396. 



t The atomic weights used in this paper are the following : — C = 12, = 16 andZn — 65. 



