FAT IN THE INTESTINAL VILLI. 223 



crystalline spots sometimes appear, indicating the solidifica- 

 tion of one of its constituents. This solid crystalline sub- 

 stance is most probably margaric acid. 



It was a part of the old physiology, that the fat must be 

 contained, not in the common cells of the cellular tissue, but 

 in proper cells, because, though fluid, it did not gravitate to 

 the lower parts of the body, like the water in dropsy. The 

 difference between the old view and the new lies merely in 

 the circumstance, that the proper cell of the fat, which was 

 formerly a conjecture, is now a recognised fact. 



There is another series of tissues which do not form per- 

 manent reservoirs for fat, in which it appears only at certain 

 times and transitorily that is to say, it disappears after a 

 while, and leaves behind no trace of change in the part. This 

 is the case in the ordinary absorption of fat from the alimen- 

 tary canal. In the passage of digested matters from the 

 intestines into the lacteals they pass through the epithelium 

 and the villi, and some hours after a meal the epithelium and 

 the villi concerned are full of fat. When a fatty substance 

 has been eaten and has been converted into an emulsion, and 

 in that state has reached the duodenum, but, more particu- 

 larly, the jejunum, the villi of the mucous membrane become 

 whitish, clouded, and thick, and on minute examination they 

 are found to contain extremely minute granules, much more 

 minute than can be produced by any artificial emulsion. 

 These granules and they occur even in the chyme come in 

 the first place into contact with the cylindrical epithelium, 

 with which every one of these intestinal villi is invested. On 

 the surface of every epithelial cell we find a peculiar border, 

 which, when the cell is seen in profile, exhibits minute and 

 fine striae ; when seen from above and upon the surface, the 

 cell seems to be hexagonal, and, as it were, dotted over with a 

 number of minute points. It has been conjectured that these 



