ILLUSTRATIVE STUDIES. 23 



9. Make a culture of yeast as follows: Pare, slice thin, and 

 boil a good-sized potato in a pint of water. After boiling till 

 it is soft mash it fine and add to this potato broth a tablespoonful 

 of sugar. Pour a little of the broth into a test-tube (i) for future 

 use and after the remainder cools dissolve in it a piece of yeast 

 cake and set the culture in a warm place. After four or five hours 

 when the culture is beady with bubbles, indicating that the yeast is 

 rapidly multiplying, remove a drop and mount it under a cover- 

 glass, having first placed a hair in the drop to prevent the break- 

 ing up of the yeast colonies by the pressure of the coverglass. 

 Study with a high power and draw a yeast colony showing 

 different stages of budding. It would be interesting to note 

 the development of the colonies from single individuals, and 

 this can be done in a hanging drop culture. Pour some of the 

 culture into a test-tube (2) and shake it vigorously to break 

 up the colonies. Clean a coverglass thoroughly in soap and water, 

 rinse it and rub it with a cloth dipped in alcohol. Place a drop 

 of broth from test-tube (i) at the middle of the coverglass and 

 dip the point of a needle first into the test-tube (2) and then 

 into the drop to inoculate it with yeast. Now invert the cover- 

 glass over a hollow slide obtainable of the dealers, having run a 

 thin film of vaseline around the border of the hollow for sealing 

 the coverglass. Bring a yeast plant into focus with the high 

 power and set the 'microscope in a warm place. Examine the 

 culture at intervals of half an hour or so. 



Instead of a hollow-ground slide a culture cell may be made 

 by spinning a ring of melted paraffin on an ordinary slide. 



