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 ^ 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^ 

 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 



