XXV.] 



LARGE INTESTINE. 



283 



Biondi's fluid (p. 81), diluted with 40 or 50 volumes of water. It requires 

 10 12 hours to stain the sections, which are then mounted in balsam. This 

 preparation is particularly valuable for studying the various forms of cells that 

 occur in the stroma of a villus. 1 



16. Absorption of Fat. (i.) Feed a frog on fat bacon ; after two days kill 

 it, and tease a portion of the mucous membrane of the intestine in normal 

 saline, or dissocinte it in dilute alcohol. Observe the isolated columnar cells 

 crowded with fine granules of oil, which are blackened on the addition of 

 osmic acid. 



(ii.) A better plan is to stain the mucous membrane in osmic acid (24 hours), 

 and embed it in paraffin. It is to be remembered,, however, that steeping the 



FIG. 273. -Villus of Dog's In- 

 testine, with Lacteal and 

 Non- Striped Muscle. L. 

 Lacteal, x 250. 



FIG. 274. Section of Intestine of 

 Frog. Absorption of fat. Osmic 

 acid. 



mass or sections of it in paraffin discharges in part the black colour of the fatty 

 granules (p. 33). 



(iii. ) Feed a rat on bread and fat of bacon ; kill it four hours afterwards by 

 means of curare. Harden the small intestine in Os0 4 . 



(H) Observe the projections like folds of the mucous membrane. The 

 columnar cells covering them are crowded with blackened particles fatty 

 granules blackened by osmic acid (fig. 274). 



17. Tubular Glands of the Intestine. In studying these, different fixing 

 fluids are used according to the animal selected (Bizzozero). 2 Amongst the 

 best fixing reagents are saturated watery solution of picric acid or picro- 

 siiljilinric acid (2 days), and wash in water (i day), subsequently hardening in 

 alcohol. This is suitable for the rectum of the mouse and dog. For the 

 duodenum, either alcohol or Flemming's fluid, or Hermann's fluid (Lesson 

 XXXV.). They are stained in safranin (1-2 hours), washed (10-15 sees.) in 

 absolute alcohol, and then stained in luematoxylin. Cleared in bergamot 

 oil and mounted in balsam. Safranin stains the nuclei of the cells, but not 

 the mucin. The latter is stained by the logwood, and one can trace it from 

 the goblet-cells passing into the lumen of the tubule. Mitosis may be 

 observed both in the protoplasmic and goblet cells. 



1 Pfliigers Archiv, Supp. Bd., 1888. 



2 Archivf. mik. Anat., p. 325, 1892. 



