Prof. Tyndall on a peculiar case of Colour Blindness. 333 



knees on the floor, and caused him to look upward at the electric 

 lamp : in this position the upper portion of the pupil was shaded 

 by the eyelid, and the coloured rings totally disappeared. I 

 then caused him to stand upon a table and to look down upon 

 the lamp : in this position the under portion of the pupil was 

 shaded by the lid, and the colours were displayed in all their 

 brilliancy. Mr. S.'s left eye was totally free from all defects of 

 this kind. I shook a little lycopodium on glass, and presented 

 it before his left eye. The system of rings this revealed to his 

 good eye was precisely similar to those presented to the other. 

 The lycopodium rings were smaller, but in other respects the 

 same as those of the right eye, with the exception of the diver- 

 gence of the latter from the circular form mentioned above. I 

 ventured to express my doubts to Mr. S. as to the retina being the 

 seat of the disease, and to comfort him with the hope that the 

 augmentation of the rings in brilliancy and magnitude pointed 

 rather to the diminution than to the increase of his malady. I 

 will leave it to physiologists to say what possible particles within 

 the humours of the eye could act the part of the spores of lyco- 

 podium -^vithout the eye; but I entertain very little doubt that 

 it is from the presence of such particles, a thin film, or some 

 equivalent optical cause, and not from any aiFection of the retina, 

 that the effects observed by Mr. S. arise. If this be the case, it 

 simply shows how necessary a knowledge of physics is to medical 

 men. I now regret that want of time prevented me from enter- 

 ing further upon the examination of the case last referred to. 



Roval Institution, 

 April 1856. 



With reference to the case of Captain C, Mr. Cooper make/ 

 the following remarks : — " In this case the symptoms are clearly 

 referable to the intense strain to which the eyes were subjected 

 for a long period, and under unfavourable circumstances — a 

 strain beyond endurance, and which seems to have deprived the 

 retina of the power of appreciating impressions. Such a con- 

 dition is little amenable to treatment. After the Great Exhi- 

 bition of 1851, instances came under my notice in which the 

 sensibility of the retina was temporarily blunted by the excite- 

 ment to which it was exposed in that brilliant scene. Here the 

 sensibility to impressions of colours was only suspended, and 

 gradually returned ; but it is to be feared, that, in the case nar- 

 rated by Pi'ofessor Tyndall, it may be regarded as extinguished : 

 the vibrations of the coloured rays produce no responsive action 

 in the nervous fibrilla;." — W. C. 



