E. HOFF-J0RGENSEN 



Standard. Stock solution: io~ 4 g. mol. of a deoxyriboside, e.g. 24 -2 mg. of thymi- 

 dine, is dissolved in 100 ml. of 25 per cent, ethanol. This solution is stable for at least 

 one year. 



Working standard: 5 X io -9 g. mol. of deoxyriboside per ml. To prepare this, 

 50 [xl. of the stock solution is diluted to 10 ml. with water. 



Basal medium, double strength (100 ml.] 



HCl-hydrolysed casein solution 



Papain-hydrolysed casein solution 



Salt A 



SaltD 



Tween 80 



Cytidylic acid solution 



Potassium acetate solution 



Thioglycolic acid solution 



Adenine-guanine-thymine solution 



Vitamin solution 



Glucose 



Z)Z-Tryptophane 



Z-Cysteine 



30 ml. 

 10 



5 

 1 



1 



1 



5 

 1 



1 



1 



3g- 



20 mg. 



20 „ 



Dissolve the glucose, tryptophane and cysteine in the previously mixed solutions, 

 adjust the pH to 67 with 1 n KOH, and add water to make 100 ml. 



Prepare the various solutions as follows : 



HCl-hydrolysed casein and papain-hydrolysed casein: as described by Hoff- 

 Jorgensen, Moustgaard and Moller (1952). 



N (00 



0.5 W /.5 2.0 2.5 

 Thymidine JO' 9 g. moi./mi 



Figure 1. Growth curve for Tbm. acidophilus R 26, 37° C, 24 hr. 



80 



