120 BACTERIOLOGICAL LABORATORY TECHNIC 



SPECIAL MEDIA 



Endo medium for the Typhoid series. Add i percent lactose to 

 plain neutral agar and i percent of the following solution: 10 c.c. 

 of 10 percent watery sodium sulphite and i c.c. of saturated 

 alcoholic solution of fuchsin, heated in the Arnold twenty minutes. 

 This should be mixed freshly each time since the medium is 

 properly colorless but becomes a pale pink on standing, being 

 then useless. It is poured into plates and allowed to cool and 

 harden thoroughly before use. 



Russell's Medium. Plain neutral agar receives i percent 

 lactose, .1 percent glucose and an indicator, either litmus or 

 Andrade. It is used as slants with a deep butt. 



The first medium is to distinguish typhoid colonies from colon 

 bacillus; pale bluish round colonies versus irregular red ones. 

 The Russell medium gives with typhoid, a colorless surface 

 growth and acid in the butt; paratyphoids give bubbles of fermen- 

 tation in the butt; colon makes distinct red slant growth and 

 much gas. 



Eggs are employed as culture media. The yolks and whites of 

 a number of eggs are shaken together in a flask and then strained 

 through a towel to remove the froth. The mixture is then run 

 into tubes and coagulated and sterilized like blood serum. On 

 this mixture the tubercle bacillus grows very well. 



These are the common culture media used in laboratories. For 

 a more technical description of the manufacture of these and 

 other media, the student is referred to books devoted to labora- 

 tory technique. 



Litmus tincture is made by adding a large handful of litmus 

 cubes to a pint of water and boiling down to one-fourth its volume. 

 This is then filtered through paper and stored after sterilization. 



The Study of the Growth of Bacteria Cultures 



Bacteria growing in groups on culture media are spoken of as 

 colonies. Aerobic bacteria may be made to grow on culture 



