136 Dr. Wollaston on Semi-decussalion 



before. I suddenly found that I could see but half the face 

 of a man whom I met ; and it was the same with respect to 

 every object I looked at. In attempting to read the name 

 Johnson, over a door, I saw only son ; the commence- 



ment of the name being wholly obliterated to my view. In 

 this instance the loss of sight was toward my left, and was the 

 same whether I looked with the right eye or the left. This 

 blindness was not so complete as to amount to absolute black- 

 ness, but was a shaded darkness without definite outline. The 

 complaint was of short duration, and in about a quarter of an 

 hour might be said to be wholly gone, having receded with a 

 gradual motion from the centre of vision obliquely upwards 

 toward the left. 



Since this defect arose from over fatigue, a cause common 

 to many other nervous affections, I saw no reason to appre- 

 hend any return of it, and it passed away without need of 

 remedy, without any further explanation, and without my 

 drawing any useful inference from it. 



It is now about fifteen months since a similar affection oc- 

 curred again to myself, without my being able to assign any 

 cause whatever, or to connect it with any previous or subse- 

 quent indisposition. The blindness was first observed, as be- 

 fore, in looking at the face of a person I met, whose left eye 

 was to my sight obliterated. My blindness was in this in- 

 stance the reverse of the former, being to my right (instead of 

 the left) of the spot to which my eyes were directed ; so that 

 I have no reason to suppose it in any manner connected with 

 the former affection. 



The new punctum caecum was situated alike in both eyes, 

 and at an angle of about three degrees from the centre ; for, 

 when any object was viewed at the distance of about five yards, 

 the point not seen was about ten inches distant from the point 

 actually looked at. 



On this occasion the affection, after having lasted with little 

 alteration for about twenty minutes, was removed suddenly 

 and entfrely by the excitement of agreeable news respecting 

 the safe arrival of a friend from a very hazardous enterprise. 



In reflecting upon this subject, a certain arrangement of 

 the optic nerves has suggested itself to me, which appears to 

 afford a very probable interpretation of a set of facts, which 

 are not consistent with the generally received hypothesis of 

 the decussation of the optic nerves. 



Since the corresponding points of the two eyes sympathize 

 in disease, their sympathy is evidently from structure, not 

 from mere habit of feeling together, as might be inferred, if 

 reference were had to the reception of ordinary impressions 



alone. 



