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 Tyndall's 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 

 sterili^r, 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 loo grammes gelatine, lo 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, ..... i part. 



Gelatine, . . . . .10 parts. ^ 



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. 



