Contributions to the Physiology of Vision. 117 



indistinct, and of a faint gleam, and the yellowish-white glare 

 at the outer side of the circular spot is black. On suddenly 

 discontinuing the pressure, a bright luminous streak flashes 

 from the inner towards the outer side. 



Dr. Purkinje has evidently bestowed much time upon these 

 experiments. It appears from some passages in his work, that 

 he began, even in his boyhood, to amuse himself with some of 

 the luminous appearances therein described. The study of 

 physiology afterwards led him to an accurate and scientific 

 inquiry, which he even pursued at the risk of health ; for, 

 although he in one passage of his work states that his experi- 

 ments had not been injurious to his sight, the circumstance of 

 his right eye being myopic, and the left near-sighted (ambly- 

 opic,) seems almost to contradict this assertion ; we ourselves 

 cannot, after a great number of experiments which we made 

 before and since our perusal of Dr. Purkinje's work, withhold 

 our conviction, that their frequent repetition may be attended 

 with dangerous effects on the eyes. On the other side, it is 

 indispensable that the experiments should be frequently re- 

 peated and varied ; for at the commencement of the inquiry the 

 observer must be quite unaccustomed to this new field of ex- 

 periment. The condition of Dr. Purkinje's sight might further 

 raise some doubts whether some of his experiments be not the 

 effects of a morbid state, rather than depending on the orga- 

 nization of the human eye. 



We have not yet exhausted the experiments which this in- 

 teresting pamphlet contains; some of those which are now 

 omitted we shall have occasion to refer to in our succeeding 



o 



papers*. 



* Since the preceding pages were printed, we have ascertained that the in- 

 teresting experiment of VIII. was first described by Steinbuch, in his Physiolie 

 der Sinne, 1811. 



