DUST GARDENS. 7 



in the laundry basket are mildewed; the "best room," 

 seldom used and darkened by drawn shades and tight- 

 ly closed blinds, becomes musty. 



What do all these things mean, or have they any re- 

 lation to each other? 



We will now see if we can answer these questions. Experiments 



with Dust 



Experiment I. Mix a little yeast with some sweet- 

 ened water and let it stand in a warm place where the 

 temperature is from 70 to 75 Fahr. Put a few table- 

 spoonfuls of beef broth or molasses water into a cup 

 or bottle and leave it uncovered in the kitchen where 

 it will be warm. Watch carefully what happens. Be- 

 fore long bubbles show on the surface of the sweetened 

 water ; perhaps you may see bubbles rising in the broth. 

 If left long enough the sweet liquid will be sour and 

 the good broth smell bad. You say the one has fer- 

 mented, the other is putrid. What has made the 

 change? You did not add anything to the mixture; 

 you only kept it warm and uncovered. 



DUST GARDENS. 



Experiment II. From any dealer in laboratory sup- The Garden 

 plies or through the doctor or druggist get a Petri dish 

 or plate. This is simply two round glass dishes, one- 

 quarter to one-half inch in depth, one just large enough 

 to fit over the other as a cover. See Fig. i. This ex- 

 periment can be made without the Petri dish, although 

 not so conveniently, as follows : 



Take a clear glass sauce dish or a finger bowl. Fig. 

 2. Cover with a piece of smooth, thin glass clear 



