72 HOW TO WORK 



examine the crumb. Still the appearance is not very definite or 

 satisfactory, and little information is gained with regard to the struc- 

 ture of the crumb or of the nature of its component particles. 



8. Next screw up the body of the microscope, and remove the 

 slide from the stage. Carry a drop of water on the tip of one finger, 

 and cause the minute crumbs of bread to be wetted without their 

 position being much altered, and carefully apply one of the pieces of 

 thin covering glass, p. 47, after breathing upon the surface which is 

 to come into contact with the fluid. The thin glass may be held in 

 forceps or between the finger and thumb, and allowed to fall upon 

 the wet crumbs very gradually by using a needle or a knife, as repre- 

 sented in pi. XXII, fig. 142. Remove the superfluous moisture by 

 the aid of the handkerchief, or with a piece of blotting paper, so that 

 no water will drop from the slide when it is placed upon the inclined 

 stage of the microscope. 



9. When the crumbs have soaked for a few seconds, give the 

 thin glass two or three smart taps so as to crush them a little and 

 make them spread out. 



10. Bring the object as near the centre of the field as possible, 

 and screw down the body of the instrument until the object comes 

 into focus. Many new facts are now learnt. 



a. A number of small, oval, circular, angular and perfectly trans- 

 parent particles are seen for the first time. 



b. The dark indefinite appearance before observed is no longer 

 visible. 



c. Each transparent particle has a sharp and dark outline. Some 

 are cracked, others exhibit irregularities of surface, while in some 

 an indication of concentric lines may be observed. These bodies 

 are starch granules or corpuscles of various sizes, modified by the 

 heat of the oven. They appear clear and transparent now they are 

 examined in water, instead of black and opaque as when they were 

 examined before in air, because the refractive power of the water 

 approaches more closely to that of the starch granule than the air. 



d. Probably some black spherical bodies or very wide and dark 

 circular rings will be observed here and there. These are air 

 bubbles, pi. XIX, fig. 122. 



n. Examine the thinnest possible shaving of deal wood or of a 

 cedar pencil, and of mahogany or oak, a fragment of blotting paper, 

 a piece of cotton and linen scraped as fine as possible, a small pinch 

 of flour, ordinary starch, common pepper, cayenne pepper, powdered 

 mustard, in the same way as the bread crumbs, taking care to allow 

 them to soak in a drop of water for an hour or more, so that they 

 may be perfectly wetted. 



