76 SOLID CULTIVATION MEDIA. 



flasks, is placed once more in a cold place for twenty-four hours. On 

 the fourth and fifth days the jelly is again steamed for a quarter of an 

 hour each day, standing in the intervals of heating in a cold place. 

 The process of sterilisation is now complete. This process is based 

 on TyndalPs principle of sterilising by the employment of discon- 

 tinuous heat; only here the partial loss of watery elements which 

 necessarily accompanies ebullition is avoided by the use of the steam 

 steriliser, which prevents all evaporation, and is equally effective in 

 producing sterility. Klein recommends that a glass cap should be 

 used to prevent the deposition of dust on the cotton wadding plug. 



Summary of Process for preparing Sterile Nutrient Jelly. 



First Day. — Steep two pounds of meat in two litres of water for 



twenty-four hours. 

 Second Day. — Extract, and filter broth. It should measure two litres. 

 „ Add ioo grammes gelatine, 10 grammes albumen 



peptone, and 5 grammes common salt. 

 „ Neutralise with carbonate of soda (sat. sol.). 



„ , Steam at 100° C. for thirty minutes. 



Third Day. — Steam thirty minutes ; filter through hot water filter 

 into stock-flasks ; steam in stock-flasks twenty 

 minutes. 

 Fourth Day. — Steam stock-flasks fifteen minutes. 

 Fifth Day. — Steam stock-flasks fifteen minutes. 



In addition to the formula given above for preparing a nutrient 

 jelly, the following will be found useful (modified from Klein) : — ■ 



Distilled water, . . . .100 parts. 



Beef peptones (Savory and Moore), . . 2 parts. 



Cane sugar, ..... 1 part. 



Gelatine, . . . • .10 parts. 1 



Dissolve, neutralise with carbonate of soda solution, and then sterilise 

 by discontinuous steaming as above. 



' Owing to the presence of sugar in this formula, a large percentage of gelatine 

 is required to render the material solid at ordinary temperatures. 



