LARGE INTESTINE. 71 



NERVE-PLEXUSES OF THE INTESTINE. 



There are two plexuses of nerves, consisting chiefly of non-medullated nerve-fibres and 

 ganglionic cells. In the intestinal walls, one plexus myentericus of Meissner lies in the 

 submucous coat; the other AuerbacKs plexus lies between the muscular coats. 



PREPARATION. Auerbach's plexus is best prepared in the following way. (a) Wash out a 

 loop of perfectly fresh small intestine of a rabbit, and distend it with the juice of a fresh lemon ; 

 ligature both ends of the gut and place it, still distended, in lemon-juice for from five to seven 

 minutes. Open the ligatures and wash it thoroughly in water, and fill it with a two per cent, gold 

 _ chloride solution ; ligature the gut as before, and suspend it for half an hour in a one per cent. 

 gold solution. Wash it thoroughly, and transfer it to a twenty-four per cent, dilution of formic 

 acid, to reduce the gold. The preparation must be kept in the dark. After reduction, it has 

 a beautiful, rich, reddish-brown colour. Wash it thoroughly and keep it in a preservative 

 fluid (p. xl). With forceps it is easy to peel off strips of the outer muscular layer, to which 

 Auerbach's plexus adheres. Mount in glycerine. The separation takes place more easily 

 after maceration for a week in the preservative fluid. This is the best method. 



(b) Another method is to use dilute alcohol, as the distending and softening medium, for 

 forty-eight hours ; then to peel off the outer muscular coat as directed above. Stain it with 

 logwood, and mount in glycerine. This gives fairly good results. 



(c) One-twentieth per cent, acetic acid may be used in the same way to fill the gut and to 

 macerate it, for thirty hours. After maceration and washing it is well to steep the gut for a 

 short time in five per cent, solution of sodic bicarbonate, to get rid of the acid. Peel off the 

 muscular coat as before, stain it with logwood and mount it in glycerine. 



EXAMINATION (L). Observe the wide-meshed plexus of fairly regular form. At the 

 nodes, groups of ganglionic cells are to be detected. Ganglionic cells are either in groups, or 

 sometimes disposed lengthwise in the flat, band-like nerve-branches. Each band has an 

 endothelial sheath. (H). The cells are very variable in size, and some of them are multipolar. 

 Nerve-branches are given off from this plexus to supply the longitudinal and circular muscular 

 coats, but their mode of termination is unknown. 



The Plexus of Meissner is prepared in a similar way, and it supplies the muscularis mucosK, 

 the blood-vessels and glands of the mucous coat. Its meshes are much wider and less 

 regular than Auerbach's. The nerve-cells are easily seen in it. 



In vertical sections of a cat's small intestine, hardened in chromic acid and spirit, groups 

 of ganglionic cells may easily be detected in the sub-mucous coat. These are the ganglia of 



Meissner's plexus. 



*/ 



THE LIVER. 



It is well to examine the liver of several animals as they differ in the complexity of 

 structure. It is best to begin with a pig's liver, and to pass to that of a rabbit, a dog or cat, 

 and then to the human organ. The liver may be hardened in several ways. 



PREPARATION. A. Chromic Acid and Spirit Mixture. Place pieces of a perfectly fresh 

 liver (pig, rabbit, cat or dog, and man), about half an inch square, in a large quantity of the 

 above fluid. Do not wash them. As the liver is very vascular, much blood exudes and 

 causes a precipitate in the fluid, which must be changed at the end of twelve hours. As soon 



