474 THE EYE - 



The lacrimal canals are lined by stratified squamous epi- 

 thelium, and possess a basement membrane as well as a con- 

 nective-tissue layer containing circularly disposed elastic elements. 

 Externally we find a layer of transversely striated muscle-fibers. 



The lacrimal sac is provided with a simple pseudostratified 

 columnar epithelium having two strata of nuclei. In it goblet cells 

 are also found. The nasal duct is lined by a similar epithelium. 

 The connective-tissue wall of the latter and that of the lacrimal 

 sac come in contact with the periosteum ; between them is a well- 

 developed vascular plexus. Stratified squamous and ciliated epi- 

 thelium have been described as being present in the nasal duct, as 

 well as mucous glands in both nasal duct and lacrimal sac. (See 

 works of M. Schultze, 72 ; Schwalbe, 87.) 



TECHNIC 



The eyes of the larger animals, after having been previously 

 cleaned by removing the muscles and loose connective tissue, are placed 

 in the fixing fluid and cut into two equal parts by means of an equa- 

 torial incision. Smaller eyes with thin walls may be fixed whole. 



Miiller's fluid, nitric acid, and Flemming's fluid are usually employed 

 as fixing agents. After fixing in one of these fluids, different parts of the 

 eyeball are imbedded in celloidin or celloidin-paraffin and then sectioned. 



The corneal epithelium is best macerated in 33% alcohol ; the 

 membrane of Descemet may be impregnated with silver. In order to 

 bring the fibers of the latter into view, Nuel recommends an injection of 

 i % to 2 ] formic acid into the anterior chamber of the eye of a dove or 

 a rabbit, after having drawn off the aqueous humor. The cornea is then 

 cut out, and fixed for from three to five minutes in osmic acid. 



The substantia propria is examined either by means of sections 

 or by means of teased preparations from a cornea macerated in lime- 

 water or potassium permanganate. The sections are stained with picro- 

 carmin (Ranvier). The corneal spaces and canaliculi may be demon- 

 strated in two ways with the aid of silver nitrate ; either the fresh cornea 

 of a small animal is stripped of its epithelium, cauterized with a solid 

 stick of silver nitrate, and then examined in water, in which case the 

 corneal spaces and their canaliculi show light upon a dark ground (neg- 

 ative impregnation) ; or the corneae of larger animals are treated in the 

 same manner, after which tangential sections are made with a razor, and 

 placed in water for a few days ; in this case the corneal spaces and their 

 canaliculi show dark upon a light ground (positive impregnation, Ran- 

 vier, 89). 



By means of Altmann's oil method casts of the corneal spaces 

 and their canaliculi may be made. Treatment by the gold method often 

 brings out not only the nerves, but also the corneal corpuscles and their 

 processes. 



Ranvier (89) especially recommends a i% solution of the 

 double chlorid of gold and potassium for the corneal nerves. The cor- 

 nea of the frog is treated for five minutes with lemon-juice, then for a 

 quarter of an hour with i % potassium-gold chlorid solution, and, finally, 

 for one or two days with water weakly acidulated with acetic acid (2 



