280 THE ORGANS 



passing through this part of the cell becomes split up into glycerin and 

 fatty acids which are united again to form fat within the protoplasm 

 of the cell. Leucocytes containing fat globules are seen throughout 

 the stroma. Within the lacteals are found fat-containing leucocytes 

 and free fat droplets of various size. It would thus seem probable 

 that the process of fat absorption consists in: (i) The passage of 

 glycerin and fatty acids through the cell borders; (2) their reunion in 

 the cell to form fat; (3) the transference of these fat globules to leuco- 

 cytes; which (4) carry them to the lacteals. In the lacteals the fat is 

 probably set free by disintegration of the leucocytes. Other fat 

 droplets — perhaps the majority — pass from the epithelial cells into 

 the lacteal without the aid of leucocytes, possibly assisted by contrac- 

 tions of the smooth muscle fibres. 



TECHNIC 



(i) The technic for the small and large intestines and rectum is the same as 

 for the stomach. Accurate fixation of the villi is difficult, there being usually 

 some shrinkage of the connective tissue of the core away from the epithelium. 



A longitudinal section should be made through the junction of small and large 

 intestine, showing the transition from the villus-covered surface of the former 

 to the comparatively smooth surface of the latter. 



To show Bruhner's glands a section of the duodenum is required. 



To show the varying shapes of the villi in the different regions, sections should 

 also be made of the jejunum and ileum. 



Solitary follicles may usually be seen in any of the above sections. 



A small Peyer's patch, together with the entire thickness of the intestinal 

 wall, should be removed, treated as above, stained with haematoxylin-eosin 

 (technic i, p. 20), or with hsematoxylin-picro-acid-fuchsin (technic 3, p. 21), and 

 mounted in balsam. 



(2) A vermiform appendix, as fresh as possible, should be cut transversely 

 into small pieces, fixed in formalin-MiiUer's fluid (technic 6, p. 7), and hardened 

 in alcohol. Thin transverse sections are made through the entire wall, stained 

 with haematoxylin-eosin or hsematoxylin-picro-acid-fuchsin, and mounted in 

 balsam. 



(3) Fat Absorption. — For the purpose of studying the process by which 

 fat passes from the lumen of the gut into the chyle vessels, an animal should be 

 killed at the height of fat absorption. A frog fed with fat bacon and kUled two 

 days later, a dog fed with fat meat, or a cat with cream and killed after from four 

 to eight hours, furnishes good material. Usually if the preparation is to be suc- 

 cessful, the lumen of the intestine will be found to contain emulsified fat and the 

 lacteals of the mesentery are seen distended with chyle. Extremely thin slices 

 of the mucous membrane of the small intestine are fixed in i-per-cent. osmic acid 

 or in osmium bichromate solution (5-per-cent. aqueous solution potassium bi- 

 chromate and 2-per-cent. aqueous solution osmic acid — equal parts) for twelve 

 to twenty-four hours, after which they are passed rather quickly through graded 



