Barrett—On Entoptic Vision. 45 
showed how measurements of the actual size of the obscurities could 
be made.! Brewster, however, only refers to the musce volitantes. 
This was followed by a lengthy and excellent paper on Entoptic 
Phenomena, by Dr. MacKenzie, published in the Kdinburgh 
Medical and Surgical Journal for July, 1845 (vol. lxiv., pp. 38, 
et seg.) The subject was then taken up by the famous Dutch 
physiologist, Donders, who largely added to the value of entoptic 
observation as a method of diagnosis of the eye. In conjunction 
with his pupil, Doncan, Donders gave admirable drawings of 
minor obscurities observed in the different parts of the eyeball, and 
discusses the whole subject in his well-known treatise on the eye.” 
A little later, Dr. Jago, of Cornwall, published two papers on the 
subject in the Proceedings of the Royal Society, and another in 
a medical Review, which, however, are more concerned with the 
medical aspect of the subject. The substance of these essays, 
with many additional observations, was issued by Dr. Jago in 
1864 in a small work entitled Entoptics.t Finally, Helmholtz 
devotes a chapter in his classical work, Handbuch der Physiologische 
Optik, to the consideration of the subject, though he does not add 
any fresh information.’ After this the subject appears to have 
1 Brewster, Trans. Roy. Soc. Edinburgh, 1843, vol.xv., p.377. See also anarticle, 
presumably by Sir D. Brewster, published in the North British Review for November, 
1856. 
* An English edition of this work was published by the New Sydenham Society in 
1864 (vol. xxii.), the excellent translation being made by the late Dr. W. D. Moore, 
of Dublin. The book is entitled On the Anomalies of Accommodation and Refraction of 
the Hye, with a preliminary Essay on Physiological Dioptrics, by F.C. Donders, m.v. 
The reference to entoptie observation will be found at pp. 197 e¢ seg. See also a paper 
by Donders, in Nederlandsch Lancet, 2nd series, 1847, pp. 365 et seq. 
8 Jago, Proc. Roy. Soc., 1855, vol. vii., p. 208; vol. viii., p. 603, also Medico- 
Chirurgical Review, 1859. 
4 Entoptics by J. Jago, m.D., Churchill, 1864. This excellent brochure by Dr. 
Jago is yery little known, and is not referred to by any writer on physiological optics 
that I haveconsulted. Ithad entirely escaped my search in compiling the Bibliography 
of this subject until quite recently, when the Rev. Dr. Abbott, s.r.r.c.p., found it for 
me in the Library of Trinity College, Dublin. Curiously enough, Dr. Jago, like other 
investigators of entoptic vision, misses the important point of the value of this 
method in the examination of cataract. 
> There is unfortunately no English translation of this great work. The French 
edition is entitled Optigue Physiologigue, and the reference to entoptic vision will be 
found in sect. 15, p. 204, of that edition. 
ge 
