44 PRACTICAL MICROSCOPY. 



Proceed to stain the intestine, with mesentery attached, with borax- 

 carmine as directed for sections, excepting that, as the mass is great, 

 it must be washed twice in alcohol after the oxalic acid. 



We have allowed the mesentery to remain connected with the gut, 

 that the former might not curl, as it would have done had it been sep- 

 arate. The preparation having reached the oil of cloves, proceed with 

 a pair of scissors to snip off a small, flat piece of mesentery. Remove 

 it to a slide, clean off the oil, apply dammar, and cover. 



The mesentery, you have learned from descriptive anatomy, consti- 

 tutes a'support for blood and lymph vessels which are in connection 

 with the intestine. The vessels are held together with a little deli- 

 cate fibrous (connective) tissue, and are covered above and below with 

 a layer of pavement epithelium. 



You will observe prominently some dark lines (the larger vessels) 

 traversing the specimen. Select a thin spot between the vessels and 

 focus H, you have a picture like Fig. 27. The field is traversed by 

 very delicate dark lines, indicating the position of the cement sub- 

 stance ; while the nuclei of the cells are pink from the carmine stain- 

 ing. 



With the fine adjustment-screw run the tube of the microscope 

 down carefully. The cement lines will disappear, and before they 

 are completely out of focus, another set of cells will appear below the 

 first set. So you may alternately bring into view the upper and under 

 layers of cells covering the respective sides of the mesentery. 



Observe the irregular shape of the cells. Note, also, that the cells 

 on one side average larger than those on the other side. You may 

 also notice in various parts of the specimen blood-vessels lined with 

 cells which are outlined with the silver staining. 



Sketch a field showing the elements as in Fig. 27, nd stain the 

 nuclei with the carmine solution. 



COLUMN AE CKLLS. 



Columnar Epithelium. 



Columnar cells are found, generally, throughout the alimentary and 

 respiratory tracts. They also line the cerebral ventricles, the urinary 

 and Fallopian tubes, the uterus, etc. This epithelium is quickly de- 

 stroyed after death and is difficult of perfect demonstration except in 

 an animal recently killed. 



Procure from the abattoir a portion of the small intestine and bron- 

 chus of a pig, and with the curved scissors snip out small pieces from 

 the mucous surface of each. Macerate in one-sixth per cent of chromic 

 acid for twenty-four hours. 



