CELLS AND THE CELL THEORY 51 



NaCL) examined with a 1/6 inch objective, will show blood cells, the red 

 cells having nucleii. 



Cartilage. Mounted sections of cartilage will show nearly rounded cells, 

 embedded in a very thick mass of cell wall, the thickened cell wall forming 

 the intercellular substance, or basis of the cartilage. 



Bone. Mounted sections will show cells lying in irregular spaces, within 

 a hard secreted mass of intercellular substance in which mineral salts have 

 been deposited. 



The cellular structure of plants may be studied by the following prepara- 

 tions: 



Cork or wood sections show plant tissue made of numerous cells of varying 

 shape. In these sections the cell walls only appear. 



A section of a growing root tip. Longitudinal sections of Podophyllum, 

 which are particularly good, should be furnished. These sections, if properly 

 stained, will show the cell contents as well as the cell walls. The protoplasm 

 and nucleus may be seen and drawn. In particularly good specimens, 

 stained with iron haematoxylin, the chromatin in the nucleus may be seen 

 with an oil immersion, 1/12 inch objective. 



For the study of protoplasm Spirogyra is a favorable object. The student, 

 after studying the normal specimen, should treat it with a little glycerine, 

 which will cause the protoplasm to shrink away from the cell wall so that 

 it can be seen. 



The movement of the protoplasm within the cell is best seen in the long 

 internodal cells of Chara or Nitella. It may also be seen in the stamen hairs 

 of Tradescantia. 



Ci'iary motion may be studied best by cutting off a bit of the edge of the 

 gill of a fresh-water clam, and examining with a high-power objective. It 

 may also be shown by scraping the roof of a frog's mouth with a scalpel 

 and mounting the scrapings in a little normal fluid. 



BOOKS FOR REFERENCE 



WILSON, The Cell in Development and Inheritance, Macmillan Co., 

 New York. 



BAILEY, Text-book of Histology, Wm. Wood, Philadelphia, Pa. 



STOHR, Text-book of Histology, P. Blakiston's Son, Philadelphia, Pa. 



DAHLGREN and KEENER, Principles of Animal Histology, Macmillan 

 Co., New York. 



MELL, Biological Laboratory Methods, Macmillan Co., New York. 



HERTWIG, Die Zelle und Die Gewerbe, Gustav. Fischer, Jena. 



CALKINS, Protozoology, Lea and Febiger, Philadelphia, Pa. 



BERNARD, Some Neglected Factors in Evolution, G. P. Putnam's Sons, 

 New York. 



