CELLS. 39 



sects, Pollen, etc., are easily mounted temporarily or permanently as 

 above. They are very commonly found in urine after it has been ex- 

 posed to the air. and their recognition is very important. 



Let me urge you to become familiar with the microscopical appear- 

 ance of the commoner objects which surround us in every-day life. 

 The most serious mistakes have resulted from ignorance of this sub- 

 ject. Vegetable fibres 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, constituted 

 .as follows (vide Fig. 23): 



A. Limiting membrane. 



B. Cell-body. 



C. Nucleus. 

 JX Nucleolus. 







FIG. 23. ELEMENTS OF A TYPICAL CELL. 



The wall consists of an apparently structureless membrane of ex- 

 treme tenuity. 



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

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



