[tubnbull] a subjective PHENOMENON OF VISION 31 



ciliary muscle. And again, in darkness the eye is focussed on infinity 

 and is consequently most flattened, and here again we have the ciliary 

 muscle most relaxed and the oscillations the slowest of all. The con- 

 vexity or flattening of the lens, as the case may be, allowing the crystal- 

 line cells to move more or less rapidly, respectively. 



Rothesay, X.B., Canada 

 June, 1904. 



Historical Review. 



• 



125. Although a somewhat careful search has been made through 

 the available literature, no mention of the phenomenon described in 

 this paper has yet been found. At the same time there are certain 

 phenomena which seem to be rather closely allied to this one, and wliich 

 I propose here to review. 



126. John Purkinje (Beitrage zur Kenutniss des Schens in sub- 

 jectiver. Hinsicht Prag. 1819) is probably the first to describe, with 

 any thoroughness, the appearance of "jumping (or springing) light- 

 points when looking at a bright surface." Purkinje in distinguishing 

 this phenomenon from the well known " mouches volantes," says, in 

 Section VII : — " If I gaze fixedly upon a large, almost blinding surface 

 (e.g., upon the evenly-clouded heavens, or close in a candle-flame) there 

 springs up bright points in a few seconds, repeatedly, in the middle of 

 the visual field. These points, without altering their position, quickly 

 disappear again, and leave black points remaining which also quickly 

 go. If. while the light points are springing up I turn the eyes toward 

 a very dark place, or close them, the phenomenon continues as before, 

 only with lessened light, and it seems as if the points were ignited 

 during the first gaze and then gradually died out. 



127. This phenomenon (as appears from the above and from sub- 

 sequent remarks by Purkinje) is undoubtedly different from that seen 

 by the writer: at the same time the phenomena may l)e allied, as Pur- 

 kinje's image appeared only after some seconds of "fixation." and in 

 the middle of the visual field. However, W. Zehender in describing 

 this (Purkinje's) phenomenon recently,^ as it appears to him, states 

 that the bright-points are immediately visil^le (and without preliminary 

 "fixing" of a "blinding surface."). He further states that "the 

 phenomenon remains the same by opened and by closed eyes, except 

 tliat in the latter case it is much less lively.'" 



^ " Klinische Monatsblatter f. Auçenheilkunde. " Mârz. 1895. The series 

 of five articles, of which this is the first, contain an excellent review of sub- 

 jective visual phenomena. (The other articles api>ear in the April, September, 

 October and November Nos. [1895] of the above magazine.) 



