252 PRACTICAL HISTOLOGY. 



teasing out either a fresh cornea, or one which has 

 been macerated for a while in weak bichromate of 

 potash, or in picric acid. The lamellse which the 

 fibrous bundles form are apparent when an attempt 

 is made to tear the corneal tissue, and they are well 

 seen, cut in different directions, in the vertical sec- 

 tions previously made. 



The corneal corpuscles are visible in the sections 

 as mere lines, each with an enlargement in the 

 middle, stretching across the containing cell-space, 

 which is fusiform in section, and is seldom filled by 

 the included corpuscle. These appearances are best 

 observed in the human cornea, but may also be 

 made out in that of the pig and those of other ani- 

 mals. But although they look like mere lines in 

 vertical section, they are, like most other connective 

 tissue cells, in reality flattened out conformably to 

 the surfaces of the lamellae, and present when viewed 

 flat great irregularities of form, and numerous 

 branching processes with which they come in many 

 cases into connection with one another. They are 

 best brought to view by the gold method, and, 

 since this also serves to show the nerves, the two 

 structures may be studied in the same preparation. 



Preparation 10. Corpuscles and nerves of 

 the frog's cornea. The brain and spinal cord of 

 a frog having been destroyed, the animal is laid on 

 the table or held by an assistant, and the membrana 

 nictitans of the eye is seized with forceps, and en- 

 tirely removed by two or three snips with fine, 

 sharp-pointed scissors. The animal is then taken 

 up and held in the operator's left hand, the thumb 

 pressing upwards under the lower jaw, so that the 

 eyes are made as prominent as possible, and the 

 point of one of the scissor blades is inserted into the 

 globe of the eye, just behind the insertion of the 

 glistening, yellowish iris. By a series of snips made 

 round the eyeball at this plane, the anterior part, 

 with the cornea, iris, and lens, is severed from the 

 posterior, and removed to a watch-glass containing 



