ELEMENTARY BIOLOGY. 



[CHAP. 



LABORATORY WORK. 



Sow some fresh baker's yeast in Pasteur's fluid 1 with 

 sugar and keep it in a warm place: as soon as the mixture 

 begins to froth up, and the yeast is manifestly increasing in 

 quantity, it is ready for examination. 



A. 



Morphology, 



Spread a little out, on a slide, in a drop of the fluid, 

 and examine it with a low power (J inch objective) 

 without a cover-glass. Note the varying size of the 

 cells, and their union into groups. 



Cover a similar specimen with a thin glass and 

 examine it under a high power (| objective). 



a. Note the size (measure), shape, surface and mode 

 of union of the cells. 



b. Their structure : cell-wall, protoplasm, vacuole. 

 a. Cell-wall ; homogeneous, transparent. 



/?. Protoplasm; less transparent; often with a few 



clear shining dots in it. 

 y. Vacuole; sometimes absent; size, position. 



1 See Appendix E, p. 494. 



