132 HOW TO WORK 



it, the cells are modified in structure and arrangement. They pro- 

 duce peculiar substances, which constitute the secretion of the gland. 

 Glandular epithelium may be obtained from the tubes or glands 

 in the mucous membrane of the stomach, from the liver, kidney, and 

 other organs. 



The mucous membrane of the stomach should be studied in vertical 

 sections, and in sections made at different depths parallel with the 

 surface. The pig's stomach is a good one for examination. A very 

 sharp knife is required. The thinnest sections may be obtained after 

 drying the mucous membrane according to the plan described in 

 page 82. The sections are to be remoistened with distilled water, and 

 made transparent by the addition of a little weak acetic acid or potash. 

 The sub-mucous areolar tissue may be very readily demonstrated 

 by removing a small piece from the under surface of the mucous 

 membrane with scissars, and tearing it up with needles. Beneath 

 the hard cuticular mucous membrane of the sesophagus, there is an 

 abundant layer of lax areolar tissue, which connectsthe lining mem- 

 brane with the muscular coat beneath, and permits the greatest altera- 

 tion of the form of the tube during the passage of its contents, to 

 take place. A small piece of this may be readily removed for 

 examination and consists of areolar tissue with vessels, nerves and a 

 few lymphatics. 



231. Vllll. Muscular Fibres. Lacteals. One of the best plans 

 of demonstrating the villi, which project from the surface of the mucous 

 membrane of the small intestine is the following: A stream of 

 water is allowed to flow over the surface so as to cause the villi to 

 fall in one direction. A clean cut is then made across the intestine, 

 and the villi caused to fall in an opposite direction by the stream of 

 water. When a very thin section is removed from the freshly cut 

 surface, one or two rows of entire villi will be readily obtained. 



The epithelium is often removed from the surface of the villi by 

 this process. Its arrangement is represented in pi. XXXII, figs. 

 207, 210, and in fig. 204 some of the separate cells are seen. 



The muscular fibres are to be shown by washing off the epithelium, 

 and treating the villi with a solution of acetic and nitric acid, com- 

 posed of about four parts of water to one of acid. Besides the 

 longitudinal muscular fibres first described by Briicke, there are 

 circular or transverse fibres, which I have demonstrated by the aid 

 of the process described in part V. Nerves and ganglia of the intes- 

 tine are referred to in p. 129. See also pi. XXXI. 



The elementary structure of the muscular coat of the intestine 

 may be demonstrated by soaking small shreds in nitric acid diluted 

 with four or five parts of water. 



