58 THE BIOCHEMISTRY OF B VITAMINS 



laboratories it was found that turbidimetric measurement of the response 

 in 18 hours or less could be used, and in one laboratory 107 titration after 

 24 to 40 hours was found to be satisfactory. 



On the basis of general experience with the two organisms, it seems 

 likely that L. arabinosus should be a more satisfactory one for pantothenic 

 acid assays than L. casei. Whether the L. casei methods are too well 

 entrenched or whether the L. arabinosus methods offer enough advantage 

 to merit their general adoption remains to be seen. 



Among the other microorganisms used for pantothenic acid assay are 

 Streptococcus lactis, 109 Streptobacterium plantarum, 110 Proteus mor- 

 ganii, 111 ' 112, 113 Streptococcus faecalis, 114 and Acetobacter suboxidans, 

 which responds to pantoic lactone and pantoic acid. 115, 116 



Chick Assay. While it would be feasible to develop an assay method 

 for pantothenic acid using the growth of any one of a number of animals 

 as a basis, only chicks have been used with any consistency. 



The assay method involves the use of a basal diet the predominant 

 ingredients of which (yellow corn meal, wheat middlings and commercial 

 casein) have been heated in the dry state to 120° C for 36 hours. This 

 heat treatment effectively destroys pantothenic acid. This mixture is 

 supplemented with minerals, sources of vitamins A, D and K and ribo- 

 flavin (whey adsorbate) . 117> 11S Chicks are kept on a normal diet for four 

 days and then placed upon the heated diet for 5 days of depletion. After 

 this they are divided into groups and fed the heated diet supplemented 

 by standard and "unknown" materials containing pantothenic acid for 

 comparison. The growth of chicks on the heated diet is very slight, but 

 in the presence of graded doses of pantothenic acid it is increased in 

 accordance with the dosage used. 



The basal diet as described is not ideal for the purpose of pantothenic 

 acid assay, but by supplementing it in accordance with newer develop- 

 ments in the field of chick nutrition it can be made the basis of a test 

 which grows more and more specific. 119 



Because of their relative ease and speed, it is probably safe to say that 

 microbiological assays for pantothenic acid have been run at least ten 

 times as often as chick assays. The microbiological tests have thus been 

 more thoroughly explored than has the chick test. In many cases the 

 microbiological and chick methods give concordant results when direct 

 comparisons have been made. Yeast and liver preparations have very 

 often given values by the chick method which are much higher than those 

 by microbiological methods. According to Willerton and Cromwell 103 

 this difference largely disappears when the material is properly digested 

 before the microbiological assay is applied. Other workers have not been 

 successful in closing this gap. 104, 107 In view of the recent findings of 



