28 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



c) Ciliated epithelium: Have the assistant give you a little tissue scraped 

 from the roof of the mouth of a freshly pithed frog. Mount the scrapings in 

 0.6 per cent salt solution, tease into small bits, cover and examine. Search the 

 field until a shimmering movement is seen; then put on the high power. Note 

 the groups of cells with one surface covered with delicate hairlike processes of the 

 cytoplasm, called cilia, which keep up a rapid vibration, sufficiently strong to 

 move small particles in the vicinity or to cause the cells themselves to whirl 

 around. You may be able to find some single cells. In that case note that while 

 the cells in groups are more or less polyhedral in shape, with flat sides, the isolated 

 cells tend to become spherical. These ciliated epithelial cells are arranged in a 

 layer lining the roof of the mouth cavity, with their ciliated surfaces toward the 

 cavity, and as the cilia of all the cells act in co-ordination, moving in waves 

 which always travel in the same direction, a current is set up in that direction, 

 as already demonstrated (experiment under II, B, 4). Draw. 



2. Muscular tissue. The cells composing muscular tissue are distinguished 

 physiologically by their property of contractility, and morphologically by their 

 long and slender form and fibrillar structure. As in the preceding kind of tissue, 

 there is relatively little intercellular substance present (Holmes, pp. 128-31). 



a) Involuntary, unstriated, or smooth muscle: Obtain a small piece of frog 

 intestine which has been macerated, mount it in salt solution, tease with needles 

 into the smallest possible bits, cover and examine. Notice that this material 

 consists of very long and slender, almost threadlike cells, running parallel, in 

 layers at right angles to each other. It is often difficult to actually isolate a 

 single one of these long cells, but if you have teased your material carefully, you 

 will generally find a few nearly separate cells along the frayed edges of the general 

 mass. Each long fiber, which is an involuntary muscle cell, possesses an elliptical 

 nucleus, usually faintly visible in the unstained material. If desired, the aceto- 

 carmine stain may be applied to render the nuclei more distinct. Draw. (It 

 may be remarked here for the benefit of the student that the figure in Holmes 

 of these cells, Fig. 35, is somewhat inaccurate in respect to their length.) 



b) Voluntary or striated muscle: Cut out a small piece from the leg muscles 

 of your preserved frog or from a recently pithed frog (the former is often bet'ter 

 for the purpose), mount in salt solution, tease carefully in the direction of the 

 long axis of the muscle until you have separated your piece into threads, cover 

 and examine. The long cylindrical objects which you will see are the muscle 

 cells, or muscle fibers, and each voluntary muscle is composed of a great many 

 such fibers. They are very large compared to the other cells which we have been 

 studying, and in fact are so long that it is impossible' to obtain a complete one; 

 hence the ends are broken. Each fiber is covered by a delicate cell wall, called 

 in this case the sarcolemma, and is crossed by conspicuous alternately light and 

 dark transverse bands (really disks, as the muscle is cylindrical). It is because 

 of these bands, which probably represent differences in the consistency of the 



