56 THE SIGNS OF LIFE [LECT. 



in the experiment of Fig. 22) has left the response to light 

 unaltered. 



On review of all these facts, I am inclined to think that, as 

 regards their action upon the retina, the two forms of excita- 

 tion act upon two distinct but closely related substances holding 

 to each other the relation of pro-substance and substance, the 

 former acted upon by electrical currents and not by light, the 

 latter acted upon by light and not by electrical currents. 



Among the tissues that give most dubious results in a first 

 rapid survey of blaze-currents, the skin was one of the most 

 notable. I therefore studied it the more closely. The next two 

 lectures will be given to the consideration of " Skin-currents." 



35. The crystalline lens. Further investigation of the blaze- 

 currents manifested by the anterior parts of the eyeball led 

 to very definite, constant, and, I may add, quite unexpected, 

 results. The observations relating to this matter were made at 

 the sea coast during the months of August and September 

 of last year principally on the crystalline lens of freshly 

 caught fish and may be most briefly described by the following 

 quotation : * 



" In the course of investigation of the effects of light and of 

 electrical excitation on the frog's eyeball, I came to the con- 

 clusion that tissues other than retinal are coeffective in the 

 response to strong induction shocks, and proceeded therefore 

 to look for blaze-currents in other living tissues. 



" The particular point that aroused my attention in the case 

 of the eyeball was the fact that the anterior half of the eyeball 

 was sometimes found to give a larger response than the posterior 

 half, and the present observations proceed from an attempt to 

 determine the principally effective part in such reaction. And 

 I may state at once, as my chief conclusion, that it is the 

 crystalline lens. 



"The eyes upon which the determination was made, in the 

 first instance, were those of fish whiting and mackerel by 

 reason of the fact that these were for a season at my disposal 



* " On the Blaze-currents of the Crystalline Lens," Proc, Roy. Soc., 

 4th December 1902, 



