82 THE TISSUES 



of serous membranes are modified connective-tissue cells rather than 

 epithelium. 



TECHNIC 



1. Simple Squamous Epithelium. — That of the lung may be demonstrated 

 by injecting with silver solution (technic i, p. 28) through a bronchus and then 

 immersing the tissue in the same solution. The lungs of young kittens furnish 

 especially satisfactory material. 



2. Simple Columnar Epithelium.— A piece of small intestine, human or 

 animal, is pinned out flat on cork and fixed in formalin-Miiller's fluid (technic 

 6, p. 7). Sections are cut perpendicular to the surface, stained with hsematoxy- 

 lin and eosin (technic i, p. 20) and mounted in glycerin tinged with cosin (p. 

 22). Little processes known as villi project from the inner surface of the intes- 

 tine. These are covered by a single layer of columnar epithelial cells. The 

 cuticulae and cuticular membrane are usually well shown. Among the simple 

 cylindrical cells are seen large clear or slightly blue-stained cells. These are 

 known from their secretion as mucous cells, from their shape as goblet cells, and 

 are classed as modified epithelium of the glandular type. These should be stud- 

 ied in their various stages of secretion, from the ceU in which only a small amount 

 of mucus is present near the outer margin, to the cell whose protoplasm is almost 

 wholly replaced by mucus. Some cells will be found in which the surface has 

 ruptured and the mucus can be seen pouring out of the cell. 



3. Stratified Squamous Epithelium. — The cornea furnishes good material 

 for the study of stratified squamous epithelium. An eye is removed from a 

 freshly killed animal and the cornea cut out and fixed in formalin-Miiller's 

 fluid. Sections are cut perpendicular to the surface, and treated as in the pre- 

 ceding. The cells are laid down in from six to eight layers. The oesophagus 

 may be used instead of the cornea, its mucous membrane being lined by a some- 

 what thicker epithelium. 



4. Transitional Epithelium. — -This is conveniently studied in the mucous 

 membrane of the bladder. Technic same as 2, above. 



5. Stratified Columnar Epithelium. — A portion of trachea from a recently 

 killed animal is treated according to the same technic. The surface cells are 

 ciliated so that this specimen also serves to demonstrate that type of modified 

 epithelium. Isolated cells or clumps of cells may be obtained from the trachea 

 in the manner described in technic 3, p. 6^. 



6. Pigmented Epithelium. — Fix a freshly removed eye in formalin- ]Muller's 

 fluid (p. 7). After hardening, cut transversely and remove the vitreous and 

 retina. The pigmented cells remain attached to the inner surface of the chorioid, 

 and may be removed by gently scraping. They may be preserved and mounted 

 in glycerin. 



7. Mesothelium. — -Part of the omentum of a recently killed animal is removed 

 and washed in water, care being taken not to injure the tissue in liandling. The 

 water is then replaced by a i to 500 aqueous solution of silver nitrate. After 

 half an hour the specimen is removed from the silver, washed in water, transferred 

 to 80-per-cent. alcohol and placed in the sunlight until it becomes light brown 

 in color. It is then preserved in fresh 80-per-cent. alcohol. The nuclei may be 



