COLUMNAR EPITHELIUM. 59 



which form the nails; and also with the flattened 

 cells from the mucous membrane of the mouth. 



Preparations 4, 5, 6,-- -The Columnar Epithe- 

 lium is most characteristically seen, and is best 

 studied as met with in the intestinal canal. It must 

 be taken from an animal (rabbit) quite recently 

 killed, as it rapidly undergoes destructive changes 

 if left after death in contact with the intestinal con- 

 tents. When the intestine is cut across at any 

 part in a recently killed animal the cut edges curl 

 outwards, and a little of the mucous membrane is 

 thus exposed. Two very small portions may be 

 snipped off this and placed, one in a few drops of a 

 one per cent, solution of osmic acid, and a second 

 in iodized serum. 1 



These two portions may be put aside for the 

 present in their respective fluids, whilst a prepara- 

 tion of the epithelium in the fresh condition is 

 made and examined. For this purpose slit open a 

 piece of the intestine, wash away the mucus and 

 intestinal contents by allowing a-little of the serum 

 from the animal's blood to drop upon the inner 

 surface, and then, with the end of a clean scalpel, 

 gently scrape the washed surface and transfer 

 what is brought away on the scalpel to a drop of 

 fresh serum upon a clean glass slide, and cover the 

 preparation, averting the pressure of the cover- 

 glass by means of a piece of hair. On examining 

 with a high power the specimen so obtained, nume- 

 rous columnar epithelium cells will be seen, some 



1 This is prepared from the amniotic fluid of the cow, by add- 

 iug to it a crystal or two of iodine, and allowing it to stand for 

 a few days, with frequent agitation, and then filtering oft' the 

 clear fluid from any precipitate that may have formed. Almost 

 any other fresh serous fluid can be used instead, but the amniotic 

 fluid is generally the most readily obtained in sufficient quantity, 

 and at the same time perfectly clear and pellucid. The serous 

 fluid serves to macerate tissues which are immersed in it, whilst 

 preserving as nearly as possible the original form of their elements. 

 The purpose of the iodine is to prevent putrefaction ; it serves 

 also at the same time to render the tissue-elements slightly firmer. 



