58 



Messrs. H. Hartridge and A. V. Hill. 



dihydroxyphenols, but not mono-phenols, is more probably due to the 

 catalysing effect of organic colloidal material than to a true enzyme as stated 

 by Gortner. The extreme resistance to high temperatures shown by these 

 extracts excludes the presence of an enzyme as generally understood. 



9. Variations in coat-colour are due probably to a quantitative rather than 

 to a qualitative difference in the pigment present, for the pigments isolated 

 from black, chocolate, and yellow rabbits show very little difference either in 

 the depth of their colour or in their chemical behaviour. 



10. Blue and the other dilute coat-colours are not caused by a lack of 

 pigment in the medulla, but by the absence of granules in the cortex, which, 

 being present in the intense colours, absorb the light which in the dilute 

 colours is reflected from the vacuoles. 



In conclusion, the writer of this paper wishes to acknowledge his indebted- 

 ness to Mr. S. W. Cole for his invaluable suggestions and help throughout 

 the course of the experiments, and to Prof. F. G. Hopkins for his kindness in 

 revising the paper. 



The Transmission of Infra-red Rays by the Media of the Eye and 

 the Transmission of Radiant Energy by Crookes and other 

 Glasses. 



By H. Hartridge, M.A., M.B., B.C., Fellow of King's College, Cambridge, 

 and A. V. Hill, M.A., Fellow of Trinity College. 



(Report of Experiments carried out for the Glassworkers' Cataract Committee of the 



Royal Society.) 



(From the Physiological Laboratory, Cambridge.) 



(Communicated by W. B. Hardy, F.B.S. Eeceived March 30, 1915.) 



Our experiments were designed to obtain evidence on the following 

 points : — 



(1) In what amount do the infra-red radiations of different wave-length 

 gain access to the deeper structures of the eye, the lens being particularly 

 considered ? 



(2) What percentage of these radiations is absorbed in transmission 

 through the lens ? 



The apparatus is shown in fig. 1 ; it consisted of a standard constant 

 deviation Hilger spectrometer, which was modified in the following manner. 



