HISTOLOGY 35 



The cells thus observed arc only the outer part of the skin of the 

 frog which is much thicker than this and will be studied in a later 

 exercise. What do you conclude regarding the relative thickness of 

 these cells as compared with their length and breadth? Measure the 

 diameter of a single cell as projected to table level. By dividing this 

 measured distance by the magnification obtained with the combination 

 of lenses in use, find the actual diameter of the cell. Make an accurate 

 drawing of several adjacent cells, including the one measured. This 

 drawing is to be 3 X the measured diameter, and the total magnifica- 

 tion is to be recorded. Indicate, also, the source of the material 

 studied. 



Exercise 29. — Columnar Epithelium. 



(c) Obtain, in a drop of the alcohol, a short piece of the frog's 

 small intestine which has been cut from a fresh specimen and soaked 

 for about twelve hours in 30% alcohol. This treatment is known as 

 maceration and makes it easy to separate the cells. Pick up the piece 

 of intestine with your forceps and shake one cut end in the drop of 

 alcohol in such a way that some of the columnar epithelial cells of 

 the mucous membrane become free in the liquid. Discard the piece 

 of intestine and place a cover glass on the drop of alcohol. Using the 

 low-power objective look for elongated cells, which will be seen singly 

 and arranged in groups. Study a favorable group. Determine the 

 exact shapes of typical cells and how the cells are fitted together. 

 In some preparations goblet cells will be found; they are so called 

 because the presence of a drop of mucus ready to be passed into the 

 intestine makes the cell resemble a goblet. What is the position of 

 the nucleus? Measure the length of a single cell as projected to table 

 level. Make a drawing of this cell (3 X its measured size) and of 

 several cells grouped together. Record the total magnification and the 

 source of the tissue. 



Exercise 30. — Ciliated Columnar Epithelium. 



(d) Obtain a small piece of the mucous membrane from the roof 

 of the mouth cavity of a recently killed frog in 0.7% salt (sodium 

 chloride) solution, or Ringer's solution. Scrape off the softer layer on 

 the mouth side of the piece, discard the tough membranous material, 

 tease apart the sticky mass that remains, and add a cover glass. With 

 the low-power objective look for movement resembling the flickering 

 of a flame in different parts of the mass which is made up of ciliated 

 columnar epithelium. The vibration of small detached particles 

 which are moving about may first attract attention. Examine, with 



