232 Intelligence and Miscellaneous Articles. 



oeption for the centre and for a point situated 80° on the outer 

 side in the visual field a difference of nearly 7 hundredths of a 

 second. That difference was notably lessened by repetition of the 

 same experiments during a month and a half ; at the end of that 

 time it was not more, for my left eye, than 2 hundredths of a second. 



(7) If exercise attenuates the difference of duration of direct and 

 indirect perception, it never annihilates it ; so that the first con- 

 stantly takes place more rapidly than the second. The influence 

 of exercise asserts itself rapidly from the first sittings ; afterwards 

 it takes effect rather slowly, and then affects direct as well as indi- 

 rect vision. 



(8) Having established at the commencement that the duration 

 of perception is the same for the left as for the right eye, I made, 

 almost every day during a month and a half, fifty determinations 

 on two well-defined points of my left eye only, excluding all other 

 points of my two retinas. I thus exercised exclusively, a very 

 great number of times, the centre of the left eye and the point of 

 the left retina corresponding to 80° in the external part of the 

 visual field (the internal part of the retina). At the end of that 

 time I could estimate the influence of exercise by comparing the 

 duration of the luminous perception on the same points in the 

 right retina, and even on other points in both retinas. That dura- 

 tion was, for the centre of the left eye 0-129 second, for the centre 

 of the right eye (not exercised) 0-143; at 80° outside for the left 

 eye the duration of perception was 0-160 second ; at 80° outside, for 

 the eye not exercised, 0-210 second. Therefore exercise had notably 

 shortened the duration of the reaction of the points experimented on. 



(9) I wished to see if the abbreviating influence had extended 

 over the left eye to points which had not been exercised. Xow the 

 duration of the reaction w as found to have been shortened in the same 

 'proportion for all the points of the inner half of the left retina (the 

 outer side of the visual field), but not for the points of the outer half. 

 Consequently the exercise of an excentric point affects the different 

 points of the same retinal hemisphere, but not those of the other 

 hemisphere. 



(10) The shortening influence had extended to the outer hemisphere 

 of the retina of the right eye, while the inner hemisphere reacted much 

 more slowly than the same part, exercised, of the left eye. 



These facts can hardly be explained, except by admitting Wol- 

 laston's theory respecting the incomplete crossing of the fibres of 

 the optic nerve in the chiasma, and supposing that the exercise of 

 one part of the retina does not act merely on that part itself, but 

 rather on the whole of the nervous centre, which receives both the 

 fibres from the half of the retina containing the exercised point and 

 the fibres from the half on the same side of the opposite retina. 



Most of these experiments were simultaneously made by my 

 assistant M. Bernardy, who aided me throughout, but, unfortu- 

 nately, being able only to utilize the right eye for these researches, 

 did not control points 8 and 10. — Comptes JRendus de VAcademie 

 des Sciences, July 10, 1882, t. xcw pp. 96-99. 



