No. 3-] ACUTE VISION IN VERTEBRATES. 449 



retinal cells, other methods such as that of Golgi or Ehrlich are 

 preferable. 



For my purposes it is necessary to obtain the eye fresh, at 

 least not later than an hour after death, and subject it to the 

 action of certain hardening fluids which will permeate and pre- 

 serve without distorting the eye. Post mortem changes occur 

 in the retina very soon, such as wrinkling in the neighborhood 

 of the fovea, which obscure its shape and size and make sec- 

 tions through it of little value. The eye is carefully oriented 

 in every case before it is removed from the head by sewing a 

 small tag to the outer layers of the sclerotic (Fig. i). In no 



Ta.j above . 



Fig. I. 



case should the eye be punctured in removal, for this invariably 

 causes wrinkling of the retina and distortion of the ball. 



I have tried many hardening fluids, but find that Perenyi's 

 fluid works the best. It not only preserves the eye with little 

 distortion, but also decalcifies all bone, thus making sections 

 even through the whole head with eyes in situ possible. The 

 different per cents of formaline which I have used have not 

 proved satisfactory, as they caused wrinkling of the retina. 



The former injection method^ is now wholly replaced by that 

 of simple immersion, which is as follows : after the eye is prop- 

 erly tagged, it is carefully removed and immersed for from 24 

 to 36 hours in Perenyi's fluid. The time depends upon the 

 size of the eye and the amount of bone to be decalcified. It is 

 then changed to 70/0 alcohol, and allowed to remain 24 hours. 

 Quite frequently when this change is made the ball caves in 

 and becomes somewhat distorted. This may be prevented or 



1 American Naturalist, January, 1896, p. 24. 



