56 



APPLIED BACTERIOLOGY 



both liquid and solid culture media, which are prepared as 

 far as possible similar to the natural soil on which they 

 lirst grew. In the following pages will be found an account 

 of the preparation of the culture media generally used by 

 bacteriologists. The preparation of these nutrient media 

 is not difficult, but it requires great care and attention to the 

 directions in order to insure success. 



Nutrient media are employed in test-tubes, small tri- 

 angular (Erlenmeyer's) tlasks, plates, or flat Petri dishes. 

 All test-tubes, flasks, etc., employed in the preparation of 

 nutrient media are thoroughly cleansed with strong nitric 

 acid, after which treatment they are well rinsed with water 

 to remove all traces of acid. The tubes are then allowed 

 to drain until nearly dry, when they are finally rinsed 

 out with a little strong alcohol, drained, and allowed to 

 dry. 



(1) Preparation of Beef-broth. — One pound of beef steak, 

 freed from fat and connective tissue, is cut 

 up and passed through a small mincing- 

 machine. The finely-minced meat is then 

 digested with 1,000 c.c. of water. It is 

 then boiled, with constant stirring, for about 

 twenty to thirty minutes in a tinned or 

 onnmellfid saucepan, which is kept well 

 broth is then strained 

 .1, and then made up with 

 to 1,000 c.c. to replace that 

 during the boiling. To the 

 DLUhLi lo ui-i^x. added 5 grammes of sodium 

 chloride and 10 grammes of peptone. The 

 latter is first rubbed up with a little of the broth in a glass 

 mortar, after which it is added to the bulk. 



The mixture is now boiled for five minutes, and then 

 very carefully neutralised with a solution of sodium car- 



Meat Press. 



