54 CONNECTIVE TISSUES. 



of a sharp pointed forceps. If that of a frog, the cornea may 

 then be mounted in glycerin without further preparation. The 

 rabbit's cornea must be prepared as before directed. In this 

 way one of the most beautiful preparations in the whole range 

 of histology is obtained. The bodies and processes of the cor- 

 puscles are seen to consist of a more or less granular proto- 

 plasm of various shades of violet. Each corpuscle contains a 

 flattened oblong, well-defined nucleus, which is of a violet 

 color, and incloses one or two large, round, dark colored nu- 

 cleoli. (Fig. 10.) Corneas stained with chloride of gold may 

 also be advantageously studied by vertical sections, and by 

 sections parallel with the surface : from such sections it is easy 

 for any one to satisfy himself that the structures seen actually 

 exist as such, and are not the products of the mode of prepara- 

 tion. It is, however, necessary to demonstrate that the cana- 

 licular network which we see with such distinctness in silver 

 preparations, corresponds to and coincides with the network 

 of branched corpuscles displayed in gold preparations, in such 

 a way as to make it certain that the latter fit into and fill 

 out the former. There are two modes of proof: a. A frog's 

 cornea is prepared and mounted, lege art-is, on the glass slide 

 (Fig. 0), and is then examined with a No. 10 immersion, objec- 

 tive, while an induced current of moderate strength is caused 

 to act upon it. After the excitation, the system of branched 

 corpuscles becomes distinguishable, and each is seen to be 

 surrounded with a clear margin. After a time this appearance 

 is lost, but can be reproduced by repeating the excitation. It 

 admits of but one interpretation, viz., that the protoplasm 

 contracts, under the excitation, in such a way as no longer to 

 fill out the space in which it is contained again occupying it 

 as soon as the contraction ceases, b. A rabbit's cornea is 

 gently rubbed with caustic until the epithelium is removed as 

 a slough. After from twenty to thirty minutes a few drops of 

 concentrated solution of chloride of gold are placed on the 

 cornea. The eye is left to itself for fifteen or twenty minutes, 

 after which time the cornea is shaved off with a razor, and 

 steeped for twenty-four hours in water feebly acidulated with 

 acetic acid. It is then not difficult to prepare from the parch- 

 ment-like cornea, with sharp forceps, thin lamella ; or to make 

 thin sections, in planes parallel with the surface, with a razor. 

 In preparations of either kind mounted in glycerin, even when 

 examined with the naked eye, three different colors may be dis 

 tinguished. There are patches of gray and others of violet: 

 and these two are separated from each other by intermediate 

 regions of a dull violet-red. Under the microscope the gray 

 parts exhibit the characteristic appearance of silver prepara- 

 tions a clear canalicular system on a yellowish-brown inter- 

 stitial substance. In the violet parts the canalicular system is 



