1901. ] on the Response of Inorganic Matter to Stimulus. 635 



will appear superimposed, arid we see an inclined cross. When 

 the stereoscope is turned towards tho sky, and the cross looked at 

 steadily for some time, it will be found, owing to the alternation 

 already referred to, that while one arm of the cross begins to be dim, 

 the other becomes bright, and vice versa. The alternate fluctuations 

 become far more conspicuous when the eyes are closed ; the pure 

 oscillatory after-effects of the strained sensitive molecules are then 

 obtained in a most vivid manner. After 

 looking through the stereoscope for ten 

 seconds or more, the eyes are closed. The 

 first effect observed is one of darkness, due 

 to the rebound. Then one luminous arm of 

 the cross first projects aslant the dark field, 

 and then slowly disappears ; after which the 

 second (perceived by the other eye) shoots 

 out suddenly in a direction athwart the first. 

 This alternation proceeds for a long time, 

 and produces the curious effect of two lumi- 

 nous blades crossing and re-crossing each 

 other. Another method of bringing out the Fig. 15. — Stereoscopic 



same facts in a still more striking manner, is d H Si f n n J° S n h °7 jocular 

 to look at two different sets of writing, with a erna lon ° V1810n# 

 the two eyes. The resultant effect is a blurr, 



due to superposition, and the inscription cannot be read with the 

 eyes open. But on closing them, the composite image is analysed 

 into its component parts, and thus we are enabled to read better with 

 eyes shut than open ! 



You will thus see how, from observing the peculiarities of an 

 artificial organ, we are led to discover unsuspected peculiarities in 

 our own. We stand here on the threshold of a very extended 

 inquiry, of which I can only say that as it has been possible to 

 construct an artificial retina, so I believe it may not be impossible to 

 imitate also other organs of sense. 



We now return to the consideration of mechanical 

 Effects of stimulus and the modification of its responses, as 

 Chemical shown in our cell. We have seen the remarkable 



Reagents. parallelism between organic and inorganic response 



under various conditions. There still remains the 

 study of the effects of chemical reagents. For drugs profoundly 

 modify the response of living substances. With respect to this func- 

 tion, they fall into three classes, some acting as stimulants, others as 

 depressors, and yet others again as poisons, by which response is 

 altogether killed. Amongst the last may be mentioned mercuric 

 chloride, strong solutions of acids, and alkalies like potash. Again, 

 drugs which in large doses become poisons, may, when applied in 

 small quantities, act as stimulants. 



Tt may be thought that to these phenomena, inorganic matter 



