i66 THE HORSE OF MR. VON OSTEN 



etc., all of which require the perception of movements. 

 This is not necessarily more difficult on account of the 

 imperfect constitution of the tissues that serve for the 

 refraction of light. Some authors even aver that this 

 facilitates the perception of moving objects. This view 

 was first advanced by the excellent ophthalmologist, R. 

 Berlin ''^ of Stuttgart. In arriving at this view he was 

 guided by the following considerations. The peculiar 

 form of astigmatism of the lens of the horse's eye, which 

 Berlin has described as " butzenscheibenformig ",* be- 

 cause it appears in the form of a series of glossy concentric 

 circles around the lens nucleus, has the property of en- 

 larging the pathway (and with it the rapidity) of moving 

 retinal images. If we take a speculum by means of which 

 a view may be had of the interior of the eye, and fixate 

 a definite point on the retina of the horse, and then 

 make a slight movement of the head horizontally, we 

 find that the point fixated moves — apparently at least — 

 toward the border of the pupil. In a normally con- 

 structed eye this seeming movement will be in a straight 

 line, while in the eye of the horse, (according to Berlin), 

 its path is curved, and therefore longer. Berlin believes 

 that the same thing which here occurs in the case of this 

 merely apparent movement, must also happen when an 

 external moving object is imaged on the horse's retina. 

 Its pathway, too, will be curved, and therefore longer, so 

 that if the head of Mr. von Osten moves past the animal's 

 eye, then the image on the horse's retina will take a 

 longer, more circuitous route than it would if the eye 



* " Butzenscheiben " are the small circular panes of green glass, used 

 in leaded windows in early days. They are high in the middle (hence 

 the name : " Butze," a protuberance) with a number of concentric circles 

 around the central elevation. — Translator. 



