556 Dr. Arthur Harden [April 28, 



WEEKLY EVENING MEETING, 



Friday, April 28, 1922. 



. Sir James Reid, Bart., G.C.Y.O. K.C.B. M.D. LL.D., 



Vice-President, in the Chair. 



Arthur Harden, D.Sc. F.R.S. 

 Vitamin Problems. 



[Abstract.] 



The existence of three vitamins, termed A, B, and C, has now been 

 firmly established, and a general idea has been obtained of their dis- 

 tribution among animal and vegetable organisms. Hitherto, com- 

 paratively little quantitative work has been done in this direction, 

 and further progress must depend on a more general adoption of 

 quantitative methods. These are at present tedious and not very 

 accurate. In the case of each of the vitamins the requirements of 

 the special animal employed serve as the unit of comparison, and 

 these vary considerably from individual to individual, so that many 

 observations are necessary if any, even moderate, degree of accuracy 

 is to be attained. Thus in the estimation of the antiscorbutic 

 potency of food materials, by the method worked out by Miss Chick 

 and her colleagues at the Lister Institute, it has seldom been possible 

 to achieve a greater accuracy than about 25-50 per cent. This 

 obviously imposes a very serious limitation on any attempts to study 

 variations in potency unless these are of a very gross order. Another 

 great difficulty inherent in this kind of observation is that when the 

 potency is low, the necessary dose of the material to be tested is 

 correspondingly high, and soon transcends what is permissible without 

 interference with other necessary conditions of the diet, such as 

 protein content, etc. Very much the same conditions hold with 

 regard to Vitamin B, especially when this is estimated by the effect 

 of the material on the growth of rats ; and, as a matter of fact, the 

 great bulk of the work carried out in America by this method is not 

 strictly quantitative, but simply leads to the result that a certain 

 ration does, or does not, suffice for the growth of a young rat. 



As regards Vitamin A, the method of Zilva and Miura promises 

 to yield moderately accurate and consistent results. This is attained 

 by keeping the experimental animals (young rats) on a diet totally 

 deficient in Vitamin A until they have ceased to grow, and then 



