218 PRACTICAL HISTOLOGY. 



villi, that the sections should be very thin indeed 

 so thin, in fact, as to include not the whole thick- 

 ness of a villus, but only a longitudinal slice ; other- 

 wise the epithelium on its surfaces interferes with 

 the view of the internal structure. With a very 

 sharp razor and considerable dexterity, this may be 

 effected even when the intestine is embedded by the 

 ordinary process, but the thin sections so obtained 

 are apt to become broken up during the process of 

 staining and subsequent washing. It is therefore 

 well to adopt for this tissue the cacao-butter process, 

 described at p. 198. A small piece is stained with 

 Kleinenberg's logwood, as there recommended, and 

 after passing through alcohol and oil of cloves is 

 impregnated with melted cacao-butter, and em- 

 bedded in a cake of the same material. There is 

 hardly any limit to the thinness with which sections 

 from a piece so embedded may be obtained, and all 

 that is further necessary is to dissolve away the in- 

 cluded cacao-butter from the sections with oil of 

 cloves and to mount them in dammar. 



Preparation 2. Fat absorption. For the pur- 

 pose of studying the course which fatty particles take in 

 passing from the cavity of the intestine into the central 

 lacteals of the villi, an animal is killed three or four 

 hours after a meal composed almost exclusively of fat (it 

 should previously have been allowed to fast for several 

 hours). On opening the abdomen the lacteals in the 

 mesentery will be found filled with chyle, and the cavity 

 of the small intestine occupied by emulsified fat which is 

 undergoing absorption. The intestine is opened at once, 

 and two or three very small pieces of the mucous mem- 

 brane are snipped off and placed in 1 per cent, osmic acid 

 solution Another minute piece is placed in a drop of 

 serum or aqueous humor and is quickly teased-out with 

 needles ; a piece of hair is added, and the preparation is 

 covered and examined. One of the portions in osmic 

 acid is allowed to remain forty-eight hours in the solu- 

 tion, and is then broken up in water. The others are 

 transferred to dilute Kleinenberg's solution, and when 

 stained throughout are embedded by the cacao-butter 



