IOO PRACTICAL HISTOLOGY. [l. 



lying over it. Notice also the highly refractile character of each 

 globule, characteristic of an oil droplet (iig. 55, 3). 



(g.} Contents. They appear homogeneous and uniform, and no 

 included body is to be seen. Each globule is, in fact, a globule 

 of oil. 



(h.) Effects of reagents. To one side of the cover-glass apply a 

 drop of acetic acid. To the opposite edge of the cover-glass apply 

 the apex of a triangular piece of blotting-paper. The blotting- 

 paper sucks up some of the milk, and the acid runs in at the 

 opposite side to supply its place. This is the process of irrigation. 

 Move the slide to bring into focus a part of the field which has 

 been acted on by the acid, and note that the corpuscles, instead of 

 floating about singly as before, are now aggregated into small groups. 

 The acid seems to have altered the surfaces of the globules, so that 

 they adhere to each other. The acid is said to act on the casein 

 envelopes of the globules, and to soften or dissolve them. This 

 preparation is not to be preserved. 



Make sketches of these objects before and after the action of 

 reagents. 



4. Potato-Starch Granules. With the blade of a knife gently 

 scrape the surface of a freshly-cut raw potato ; place the matter 

 so obtained in a drop of water on a slide. Remove any coarse 

 fragments, and apply a cover-glass. Focus the object (H). 



(.) Observe that the granules (fig. 53) -are ovoid bodies of 

 unequal size, not equal at the two ends, clear, and with a sharp 

 outline. Near the smaller end of each granule 

 notice a small spot, the " nucleus " or liilum, round 

 which are concentric layers, giving rise to the 

 appearance of fine concentric lines arranged with 

 relation to the nucleus. The lines are more 

 numerous on one side of the liilum than the other. 

 Sketch two or three of the granules. 



(!>.} Irrigate the corpuscles with a diluted solu- 

 tion of iodine in iodide of potassium. Each 

 g ranu ^ e becomes blue as the iodine reaches it. 

 This is due to the formation of iodide of starch. 

 If the iodine be too strong the granules appear black. 



5. Rice-Starch (H). Examine a little rice-starch in the same 

 way. Notice the much smaller irregular granules. Each granule 

 is polygonal, mostly five or six sided. The granules are stained blue 

 by iodine (fig. 54). Make sketches of the starch corpuscles. 



6. Gamboge and Brownian Movement (H). Rub up a small 

 piece of solid .gamboge in water, until the Jatter, has a faint yellow 

 appearance. Place $ $*%> oft a siUfle^ cover, -ah& cxaTiiine. 



(a.) Observe 'granules of 'various "sizes 'and shapes floating in the 



