STRUCTURAL ELEMENTS CELLS 49 



as before noted. They are very commonly found in urine 

 after it has been exposed to the air, and their recognition is 

 very important. 



Let me urge you to become familiar with the microscopical^ 

 appearance of the commoner objects which surround us in every- 

 day life. The most serious mistakes have resulted from ignorance 

 of this subject. Vegetable fibers have been mistaken for nerves 

 and urinary casts, starch granules for cells, vegetable spores for 

 parasitic ova, etc. 





STRUCTURAL ELEMENTS 



Certain anatomical structures, of a more or less elementary 

 nature, are united in the composition of organs. These structural 

 elements will, with propriety, first claim notice from us. 



CELLS 



A typical cell is a microscopical sphere of protoplasm, consti- 

 tuted as follows (vide Fig. 26) : 



A. Limiting membrane. 



B. Cell-body. 



C. Nucleus. 



D. Nucleolus. 





D 



FIG. 20. ELEMENTS OF A TYPICAL CELL. 



The wall consists of an apparently structureless membrane of 

 extreme tenuity. 



The cell-body may be either clear (jelly-like), granular, or 

 fibrilliated. It contains an albuminous substance called protoplasm. 



The nucleus is a minute spherical vesicle, with a limiting mem- 

 D 



