118 BACTERIOLOGY. 



paste, and is heated in the steam steriliser for half an hour for three 

 successive days. 



(E) PREPARATION AND EMPLOYMENT OF BREAD-PASTE, VEGETABLES, 

 FRUIT, WHITE OF EGG. 



Some micro-organisms, more especially mould fungi, grow very 

 well on bread-paste. This is prepared by removing the crust from 

 slices of bread and drying them in the oven. They are then 

 broken up, and reduced to a fine powder with a pestle and mortar. 

 Small, carefully cleansed, conical, or globe-shaped flasks are plugged 

 with cotton-wool and sterilised in the oven. When cool, a small 

 quantity of the powder is placed in them, and sterilised water added 

 in the proportion of one part to every four of the powder. The 

 paste is sterilised by steaming in the steriliser at 100 C. for half an 

 hour for three successive days. The flasks can be reversed, and may 

 be inoculated with a platinum needle. 



Boiled carrots and other vegetables, and various kinds of stewed 

 fruit, are also occasionally employed for the cultivation of bacteria. 

 The sterilisation of these media must be carried out on the principles 

 already explained. 



White of egg may be solidified in shallow glass dishes, in the 

 steam steriliser. After inoculation the dishes should be placed 

 in a damp chamber. 



LIQUID MEDIA. 



(F) PREPARATION OF STERILISED BROTH, LIQUID BLOOD SERUM, 

 URINE, MILK, VEGETABLE INFUSIONS, AND ARTIFICIAL NOURISH- 

 ING LIQUIDS. 



Nutrient liquids are still largely employed. For inoculation ex- 

 periments when the presence of gelatine is undesirable, for studying 

 the physiology and chemistry of bacteria, and when for any object 

 a rapid growth of micro-organisms is necessary, the employment 

 of liquid media is not only advisable, but absolutely necessary. 

 Liquid media comprise two distinct groups natural and artificial. 

 Natural media include meat broth, blood, urine, milk, and vegetable 

 infusions ; artificial media are solutions composed from a chemical 

 formula representing essential food constituents. 



Broth may be made from beef, pork, chicken, or fish in the 

 manner which has been described for the preparation of nutrient 

 gelatine, simply with omission of the gelatine. After the process 



