GENERAL PHYSIOLOGY OF THE FROG 29 



muscle substance, that voluntary muscle is called "striped" muscle. A longi- 

 tudinal striation may also usually be seen, indicating that the muscle fiber is 

 really composed of a number of much smaller longitudinal fibers, known as 

 fibrillae or sarco styles, which are bound together in the same sarcolemma. Each 

 muscle fiber contains a number of slender nuclei, located near the surface, just 

 under the sarcolemma. In order to see them it will generally be necessary to 

 apply the aceto-carmine stain. Since the young muscle cell possesses but a 

 single nucleus, and since the others are produced by the division of this nucleus, 

 it is probable that the adult muscle fiber is not a single cell but a number of cells 

 with no cell walls between. Such a multinucleate structure is called a syncytium. 

 Draw a muscle cell showing all structures. 



3. Connective tissue. In this type of tissue, the cells are much reduced 

 and few in number, and the greater bulk of the tissue consists of intercellular 

 substance. The function of the connective tissue is that of supporting and 

 binding other parts and tissues. It is therefore exceedingly widespread (Holmes, 

 pp. 123-28). 



a) White fibrous or collagenous connective tissue: This is the white weblike 

 material binding the muscles of the frog together or forming the partitions 

 between the subcutaneous lymph sacs. Remove some from either of these places 

 of your preserved 'frog, spread it out carefully on a slide so as to make a very 

 thin layer, add salt solution, cover and examine. It consists for the most part 

 of long, slender, wavy fibers, running in all directions. These are the white or 

 collagenous fibers (so called because when boiled they form glue) ; they are very 

 tough and inelastic. Another type of fiber, the yellow elastic fibers, is present 

 in small numbers, distinguishable by the fact that they run straight and singly, 

 not in bundles as do the white ones. The fibers of connective tissue are not 

 cells, and are probably not living, but they are the intercellular products of the 

 real connective tissue cells. In order to see these latter, apply the aceto-carmine 

 stain, and note after a few minutes the oval nuclei of the connective tissue cells 

 staining deep pink or red, scattered among the fibers. The acetic acid in the 

 stain will also tend to dissolve the white fibers, making the yellow elastic ones 

 more distinct. Cells and fibers are imbedded in an invisible, clear, gelatinous 

 matrix which is also secreted by the cells. Draw a small portion of the tissue, 

 showing fibers and nuclei. 



b) Cartilage: Have the assistant slice off with a razor a thin piece of cartilage 

 from the end of the one of the long limb bones of a recently pithed frog, mount 

 in salt solution, cover and examine. The prepared slide "Frog cartilage" may 

 also be used. Cartilage consists of a clear matrix which is much more dense and 

 firm than in the previous type of connective tissue. In this matrix are rounded 

 spaces or lacunae, at intervals, which are completely filled in the living material 

 by the cartilage cells, which secrete the matrix. When two or more cells are 

 contained in one lacuna, they have originated through the division of a previous 



