﻿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. 



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

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

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

 cells, and their union into groups. 



2. Cover a similar specimen with a thin glass and 

 examine it under a high power (1 objective). 



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

 of union of the cells. 



b. Their structure: sac, protoplasm, vacuole. 

 a. Sac; homogeneous, transparent. 



(3. Protoplasm; less transparent; often with a few 



clear shining dots in it. 

 y. Vacuole; sometimes absent; size, position. 



1 Pasteur's fluid : 



Potassium Phosph 20 parts. 



Calcium Phosph 2 ,, 



Magnesium vSulphate 2 ,, 



Ammonium Tartrate 100 ,, 



[Cane Sugar 1500 ,,] 



Water , ^57*3 ,, 



10,000 parts. 



The sugar is to be omitted when Pasteur's fluid "without sugar" is 

 ordered. Pasteur himself used actual yeast ash; the above constituents 

 give an imitation ash, which, with the ammonium salt and sugar, 

 answers all practical purposes. 



