PROBLEM 19 49 



4. Note. — The jointed, vertical pillar gives attachment to the arm, support- 

 ing the main tube of the instrument. 



What are the advantages of having the pillar jointed? 



5. Note. — Extending forward from the pillar below the arm is the stage, on 

 which is placed the object to be examined. 



Describe the location of the perforation in the stage. What is its use? What 

 is the use of the revolving wheel, or diaphragm, pivoted to the stage? 



6. NOTE. — Below the stage is a movable bar (P) , carrying the mirrors or 

 reflectors. 



In how many different directions can you move the mirrors? What is the 

 advantage of having them movable ? What kind of surface do the mirrors respec- 

 tively show? What is the use of the mirrors? 



7. Note. — A hollow cylinder containing two lenses fits into the upper 

 end of the tube. It is called the eyepiece or ocular (G). 



Why is the name eyepiece applied? 



8. Note. — Small brass mounts, each containing several lenses, are attached 

 to the tube at its lower end ; they are the object lenses or objectives (F, P). 



Why is the name objective given to these lenses? How many objectives are 

 there in your microscope? 



9. Note. — The low power (a slightly magnifying objective) has a short and 

 broad mount. The high-power objective has a long and narrow mount. 



What fractional numbers do you find on the mount of the high and the low 

 power objectives, respectively? 



10. Note. — The objectives are attached to a revolving device, the nose piece. 

 What are the advantages of a revolving nose piece? 



11. NOTE. — To obtain a clear image of the object under examination, we must 

 be able to vary the distance between the lenses and the object ; that is, to focus 

 the instrument. The microscope is brought into focus by slightly turning either 

 of the large wheels placed at the top of the arm near the tube. 



Why are these wheels called the coarse adjustment ? (Turn one of them gently !) 

 What movement results? 



12. NOTE. — The milled head of the fine adjustment is found at the top of the 

 pillar. 



Carefully turn the fine adjustment back and forth. (No more than half a turn 

 in either direction!) Why is this adjustment called "fine"? 



Problem 19: To determine the unit of structure in plants 

 and animals. 



Materials. — Oriion skin, sciapings from mouth, compound 

 microscope, slides, methyl blue. 



Method. — Scrape some cells from the inside Hning of the cheek 

 with a sterilized knife. Mount in water. Stain with methyl blue. 

 Onion skin may be used and stained with methyl blue or iodine. 



NOTE. — A cell is a small living structure made up of living matter (]}rotoplasm) 

 containing a portion which in part readily absorbs stain. This structure is called 

 the nudeus. A cell is usually bounded by a cell wall or cell membrane. 

 HtTNTEB LAB. PEGS. — 4 



