8 HOUSEHOLD BACTERIOLOGY. 



enough to see through readily and large enough 

 to entirely and ' tightly cover the dish. After 

 washing well, place both together in a pan in a cool 

 oven and gradually raise the temperature until it is hot 

 enough to bake bread or to yellow a piece of white 

 paper in half a minute. Let them bake for an hour 

 or more. Then open the oven and place the pan 

 where the dish may cool slowly. When cold take 

 out, without removing the covering plate, and put 

 round both dish and plate a strong rubber band, or tie 

 them together with a string. 



This we will call our garden-plot. But a garden is 

 of little use without something growing in it, and for 

 this soil is required. 



FIG. 1. PETRI DISH FOR PLATE CULTURES. 



Soil for the For the soil take the following recipe : Chop finely 

 one-quarter pound of lean, juicy beef. Mix this with 

 one cup of warm water. Heat in double boiler, stir- 

 ring often until water in water pan has boiled fifteen 

 min-ites. Remove inner dish, place directly over the 

 fire and allow broth to boil ten or fifteen minutes. 

 Clear by straining through two or more thicknesses of 



