VITAMIN B (Bi) 103 



unit of the vitamin; and from this the number of such units of vitamin 

 B contained in a gram, a kilogram, a pound, an once, or a lOO-calorie 

 portion of the food can readily be calculated. 



In much of the work of the past in which special attention was 

 being given to the quantitative aspect, a test period of 8 weeks has 

 been used in the belief that this was safer, and apt to be more accurate, 

 than any shorter period ; but in view of recent evidence that after 

 several weeks on the basal diet other vitamins, not yet well defined, 

 may begin to be limiting factors also, and thus complicate the measure- 

 ment of vitamin B, it now seems perhaps better to base the quantitative 

 comparison upon the rate of gain during a period of four weeks be- 

 ginning at the end of the "depletion period" ; or, if the body weight 

 should decline for a few days after this, then the measured test period 

 may be counted as beginning at the minimum point of the weight 

 curve during the first week of the feeding of the test portions of the 

 material under investigation. (Attention should, perhaps, be called to 

 the fact that the "unit" here suggested is not identical with that for- 

 merly used by one of us: Sherman, 1926.) 



Many of the precautions advised to insure accuracy in vitamin A 

 determinations (see Ch. V) are probably equally applicable to this 

 method for determining vitamin B. In this connection attention may 

 be called to work which, while published before the clear differentia- 

 tion of vitamin G (Bq), is yet applicable to the control of the present 

 method for the measurement of vitamin B (Bi) values: Sherman and 

 McArthur, 1927; Sherman and Gloy, 1927. 



Chick and Roscoe (1929), in the method which they have adopted 

 for the assay of vitamin Bi, use washed brewery yeast autoclaved at 

 120° C. for 5 hours as their source of vitamin B2, although admitting 

 that this occasionally carries traces of vitamin Bi and also has a 

 tendency to cause diarrhea. The basal diet for the assay of either vita- 

 min Bi or B2 consists of purified casein 10, rice starch 30, cottonseed 

 oil 7.5, McCollum salt mixture (185) 2.5, and distilled water 50 parts, 

 the whole being cooked in a double boiler for 3 hours at 100° C. to 

 prevent refection. Cod-liver oil is administered separately in daily doses 

 of 3 to 5 drops (0.05 to 1 gm.) depending upon the size of the animal. 

 In the assay of vitamin Bi the young rats are placed at weaning on 

 the basal diet plus the cod-liver oil and when growth has ceased are 

 given the material to be tested as a supplement. The unit of vitamin 

 Bi which they have selected is the amount which will restore growth 

 and induce a weekly increase in weight of about 10-14 grams under 

 these conditions. 



