ii.J THREE TYPES OF RESPONSE 29 



reason of the physical lost-time of the suspended magnets and 

 mirror. With the capillary electrometer, which has no appreci- 

 able lost-time, the latency comes out at about 0.15 second still 

 a very considerable delay, and indicative of a rather surprising 

 physiological inertia of the retinal organ.* (See Fig. 12.) 



I had the curiosity to repeat the experiment under precisely 

 similar conditions on an oxidised copper plate, which, as is well 

 known, is acted upon by light, and gives, therefore, electrical 

 currents in response to illumination (Fig. 61, p. 159). There 

 was no detectable lost-time, either by galvanometer or by 

 electrometer a fact which is of interest in the present con- 

 nection merely in that it bears witness to the correctness of the 

 retinal data taken by the same apparatus. 



When it has been clearly recognised that the regular and 

 typical response of the fresh uninjured eyeball is of positive 

 direction, i.e., directed from fundus to cornea, we may proceed to 

 consider, without losing our way amid a tangle of abnormalities, 

 the varieties of character that present themselves, not merely in 

 the response to light, but in the response to mechanical and to 

 electrical stimulation. And when we have considered such 

 varieties, we shall return to the consideration of the above 

 described typical positive response, and recognise that this posi- 

 tive response is in all probability the algebraic sum of two 

 opposite and not perfectly congruent electrical changes. The 

 terminal positive effect at the closure of illumination, which 

 must have been to us at first sight a somewhat puzzling feature, 

 will then become intelligible to us. 



1 6. Three types. For the sake of distinct description, I 

 have classified the response to light as falling into one or other 

 of three types : 



I. Positive response of the first type, characteristic of the 

 normal fresh uninjured eyeball. 



II. Mixed responses, characteristic of transitional states 

 between types I. and III. 



III. Negative response of the third type, characteristic of the 

 compressed or partially injured eyeball. 



* Gotch has recently and independently made similar observations (see 

 References). 



