THE GENERAL STBUCTUBE OF THE HUMAN BODY 5 



cells from the mouth 



liver cells 



-^^ 



a. Name, now, two parts of a cell from the membrane 



lining the mouth. 

 h. State the form and position of the cell nucleus. 



3. Make a drawing of two of the cells described above (each 



cell to be represented about an inch in diameter). 

 Label cell body and cell nucleus. 



4. (Optional.) Demonstrate by the use of prepared slides, pic- 



tures, or charts that the brain, the intestine, and other organs 

 of the body are composed of cells (Fig. 3). 



5. Cells and protoplasm.^ — Under the microscope cells at 

 first appear to be only plane surfaces surrounded by lines 

 (Fig. 3). In reality, 

 however, each cell 

 has not only length 

 and breadth, but 

 also thickness. 

 Cells in animals 

 and human beings 

 differ from those in 

 plants in never hav- 

 ing cell walls of cel- 

 lulose, and often cell 

 walls are entirely 

 wanting. If pres- 

 ent, the cell wall is so transparent that it is possible to look 

 through it and see the cell body and nucleus within. 



The discovery of these minute bodies of which organs are 

 composed was not made until about the middle of the last 

 century (1848). With the rather imperfect microscopes 

 then in use the two discoverers, Schleiden and Schwann, 

 could see the walls only, and they did not know, as we now 



' Because of the importance of emphasizing cellular structure, 

 the substance of §§42 and 43, " Plant Biology," are here inserted. 



Fig. 3. — Cells from tissues of body. 



