. 



UNIVERSITY 



71 



sterilization. It is very useful in cultivating the bacilli of 

 tuberculosis and diphtheria. 



Sugar -agar. Before sterilizing, i per cent, of either dextrose, 

 lactose, saccharose or other sugars may be added to agar. 

 In this case the agar should be prepared from sugar-free broth 

 as in the preparation of broth to which the sugar, are added. 

 With media containing sugar, litmus forms a useful indicator 

 of the production of acid. Enough tincture of litmus is used 

 to give the medium a blue color before sterilization; the litmus 

 is somewhat unstable and prone to change its color during 

 sterilization. Azolitmin is now recommended in place of 

 litmus (see below). Neutral red may also be added in the 

 same manner; its color is changed by certain bacteria and 

 not by others (see bacillus of typhoid fever and bacillus coli 

 communis, Part IV.). To i liter of nutrient agar, add i gram 

 of dextrose and 0.05 gram or 10 c.c. of a saturated aqueous 

 solution of neutral red. Sterilize as usual. 



The committee on Standard Methods of Water Analysis, 

 Am. Pub. Health Assn.* recommend the following: Lean 

 meat should be used, not beef extract, as a basis for the various 

 media; sodium chloride shall not be used for water analysis; 

 Witte's peptone shall be used; gelatin must be the best French 

 brand, and the 10 per cent, solution after its preparation as a 

 culture medium shall not soften at 25 C. All sugars shall b,e 

 chemically pure, glycerin when used must be double distilled. 

 In place of litmus, where this is used, azolitmin shall be 

 substituted. 



Potato. The potatoes are washed, a slice is removed 

 from each end, and with an apple-corer or cork-borer a cylinder 

 is cut out.f This cylinder is divided diagonally into two pieces. 



*Jour. Inf. Diseaes, Supplement No. i, May, 1905, p. 104. 



fBolton. The Medical News. Vol. L, 1887, p. 318. A Method of Pre- 

 paring Potatoes for Bacterial Cultures. Roux. De la Culture sur Pomme de 

 Terre. Annales de I'lnstitut Pasteur. T. II., 1888, p. 28. Globig. Ueber 

 einen Kartoffel-Bacillus mit ungewohnlich widersland;fahigen Sporen. Zeit- 

 schrijt jur Hygiene, p. 322, 1888. 



