Slime Moulds, Bacteria, and Yeasts. 255 



placing the other half beside it under the bell jar. Record 

 your observations in your notes. Thread-like growths may 

 appear among the spots of bacterial colonies; these are 

 Fungi, which are higher in the scale of life than the bacteria. 

 They should be left to form their spores undisturbed for 

 use in a subsequent study. 



147. Put milk into a clean flask, plug tightly with a wad 

 of cotton, and steam in a steamer for half an hour on each 

 of three successive days. The milk should be found to 

 continue sweet for an indefinite period. 



148. Remove on the point of a needle a very small por- 

 tion of bacterial material from Observation 146 (or take a 

 small drop of the culture of Observation 145) and place it 

 in a drop of water at the center of a glass slip, and stir the 

 drop with a needle to thoroughly distribute the bacteria. 

 Let the water evaporate, and then pass the slip, prepara- 

 tion side up, three times through the flame of an alcohol 

 lamp, each passage through the flame occupying about 

 one second. This fixes the bacteria to the slip. Place a 

 drop of a i Jfc aqueous solution of fuchsin on the prepara- 

 tion, and wash it off after a minute in running water, or 

 by moving it about in a dish of water. Then pass the 

 preparation two or three times quickly through 60 Jfe 

 alcohol to decolorize the background. Let the prepara- 

 tion dry and mount in Canada balsam (see page 390). 

 Draw the different forms of bacteria clearly brought out 

 by the stain. 



149. Soak a piece of yeast cake over night in a saucer 

 of water, and then mount a very small portion of it in a 

 drop of water under a coverglass. Spread the yeast out 

 in a thin layer by giving the coverglass a circular motion 

 by means of the point of the finger, covered with a clean 

 cloth to avoid smirching the coverglass. Examine with a 



