8 THE ESSENTIALS OF HISTOLOGY. 



around a minute spot which is generally placed eccentrically near the smaller 

 end of the granule. Sketch two or three starch-granules. 



Notice the appearance of air-bubbles in the water. If comparatively 



FIG. 6. ORGANIC MATTERS FREQUENTLY PRESENT IN DUST. (Heitzmann.) 



S, fibres of silk ; C, of cotton ; L, of linen ; W, of wool ; F, feather ; St, starch -granules ; Cr, 

 cork ; 0, torulae ; M, mycelium or threads of mildew ; Me, micrococci ; B, bacteria ; Lt, 

 leptothrix filaments (500 diameters). 



large they are clear in the middle, with a broad dark border due to refraction 

 of the light ; if small they may look entirely dark. 



2. Examine some brewers' yeast which has been grown in solution of 

 sugar. Observe the yeast-particles or torulse, some of them budding. Each 

 torula contains a clear vacuole, and has a well-defined outline, due to a 

 membrane. Sketch two or three torulse. 



