170 THE HORSE OF MR. VON OSTEN 



would involve even fewer elements than the straight 

 one. And finally, when the movement which the horse is 

 to perceive, does not occur in a straight line but in the 

 form of a curve, (which will generally be the rule), 

 then the astigmatism will tend in many cases to decrease 

 the curvature of the image's path on the retina, and 

 sometimes even obviate it entirely. In all these cases, 

 on Berlin's own theory, the perception of the movements 

 would be hindered rather than aided.* 



* For the benefit of specialists I would say the following in addition 

 to the more general remarks just made. For the most part, the deter- 

 minations of refraction made on the eye of the horse are still rather 

 unreliable. In sciascopy there is a dispute among investigators con- 

 cerning ambiguous shadows, and in the use of the refraction-ophthal- 

 moscope no definite region of the eye's background has been adhered 

 to by the various investigators. It appears that Riegel, whose diligent 

 researches mentioned on page 164 were published in 1904, knew nothing 

 concerning the round area in the horse's eye, discovered by I. Ziim " in 

 1902. Also, if so great a degree of astigmatism is really the rule as is 

 emphasized especially by Hirschberg*^ and Berlin,'^* then the simple 

 refractive index usually given — sometimes within a half diopter- 

 would be meaningless. Berlin *5 and Bayer *' believe the vagueness of 

 the retinal image resulting from the astigmatism, is offset by this : that 

 the oval pupil functions as a stenopaic slit. In view of the width of the 

 horse's pupil this appears to me to be rather hypothetical. 



Concerning Berlin's theory of deflecting astigmatism I would say the 

 following : Of the two ophthalmoscopic signs mentioned as being 

 characteristic of this form of astigmatism, — the concentric circles and 

 the arcuate deflection of the pathway of the fixated points, — when there 

 is a movement of the eye of the observer (or of the eye observed), ac- 

 cording to Berlin the former is not so constant as the latter. So far as 

 I know, the concentric ring formation is mentioned only by Bayer*' and 

 Riegel,*' and is said to occur principally in horses with myopic vision— 

 and hence, relatively, in a minority of cases. Judging from the particu- 

 lars, we are inclined to believe that a case of " Butzenscheiben "—lens 

 reported by Schwendimann *8o jg ;„ reality a case of senile sclerosis. 

 Berlin repeatedly warns us against mistaking the one for the other."' 

 The arcuate deflection, on the other hand, has not been mentioned else- 



