36 THE FROG 



the high-power objective, a place where this movement appears. The 

 cells are rather short columns which tend to be pointed at their inner 

 ends and blunt at their outer, ciliated ends. However, when the 

 living cells are torn apart they contract and appear as globular or 

 bluntly cone-shaped bodies. The cilia, which are very delicate proc- 

 esses, cannot be seen individually but may be recognized as a flicker- 

 ing zone bordering the free ends of the cells. Observe the effect of 

 the cilia upon small particles which may be in the preparation. Look 

 for dying cells whose cilia are no longer in motion or have disappeared. 

 In such a cell the relatively large nucleus can be distinguished. 

 Measure the diameter of such a cell as projected at table level and 

 draw it and several other cells (3 X projected size). Record the 

 total magnification and source of the tissue. 



(e) Observe, in a demonstration of the roof of the mouth cavity 

 of a frog or the gill of a mussel, the action of the cilia upon small 

 objects and imagine their action upon microscopic particles. What is 

 the function of these cilia? Examine, also, a demonstration of a per- 

 manent preparation of a section of the trachea, mussel gill, or other 

 suitable material to see the cilia clearly. 



Exercise 31. — Connective Tissue. 



(f) Spread out a small piece of connective tissue on a slide in a 

 drop of water, tease the edges, and add a cover glass. This tissue is 

 most readily obtained from between the muscles of the leg in a pre- 

 served frog or from the inside of a cat's skin which has been preserved 

 in formalin. Connective tissue has widely separated cells with a large 

 amount of intercellular material in the form of fine fibers. These 

 fibers are of two kinds: white fibers, very fine ones which run in 

 wavy bundles, and elastic fibers, which are thicker, occur singly, and 

 are straight. In some preparations one type of fiber will predominate 

 and in some the other. In many preparations it may be hard to 

 distinguish the two kinds. The cells of connective tissue are not easy 

 to demonstrate but they may be seen by staining. Remove the cover 

 glass and stain the piece of connective tissue with methyl violet for 

 about a minute. Rinse in a drop of water and mount in a clean drop 

 of water. If bundles of white fibers are seen, measure as projected 

 at table level and draw (3 X measured size). Record total magni- 

 fication and source of material. 



Exercise 32. — Cartilage. 



(g) Examine sections of cartilage that have just been cut from 

 the head of the femur of a recently killed frog and placed in 0.7% 



