96 THE VITAMINS 



change in their food or the administration of vitamin in any form 

 (Kon and Drummond, 1927; Kon, 1927), and temporary cures have 

 been reported effected by a variety of substances which may bear no 

 relation (in chemical nature or normal nutritional function) to the anti- 

 neuritic vitamin. This being the case it necessarily foUovi^s that neither 

 the positive nor the negative results obtained in "curative" experi- 

 ments can be entirely conclusive in any individual case. Safe conclu- 

 sions can be drawn only from a preponderance of the evidence re- 

 sulting from numerous experiments conducted under rigidly controlled 

 conditions. Peters and coworkers (Peters, 1924; Kinnersley and Peters, 

 1925, 1927, 1928; Kinnersley, Peters and Reader, 1928) describe their 

 technique for the use of the pigeon as a reagent. These papers will 

 repay careful study by those interested in this method. Under well- 

 controlled conditions there is usually a quantitative relationship between 

 the time of protection after cure and the amount of curative dose 

 given. 



With a well-chosen basal dietary fed to an animal of suitable species 

 and of standard age and weight, the amount of the food under investi- 

 gation which will be needed for protection from deficiency disease or 

 for support of a standard rate of growth will be inversely propor- 

 tional to the concentration of vitamin in the food, provided no dis- 

 turbing factor is allowed to enter into the test. This minimum allow- 

 ance of the food in question may be determined either in terms of 

 the weight required per day when the test food is fed separately from 

 the rest of the diet, or of the proportion in which the test food must 

 enter into the food mixture in order to make the ration adequate. In 

 either case the total food intake should be determined and the adequacy 

 of the diet in respect to all other nutritive requirements should be 

 assured. Obviously in either case the determination of the "minimum 

 protective dose" of the food or of the minimum allowance for support 

 of a standard rate of growth is likely to require a series of experiments 

 in which the quantity or proportion of the test food is systematically 

 varied while all other conditions are held constant. Such a series of 

 quantitative experiments is naturally much more exacting than the 

 few tests which would suffice to demonstrate the presence of the vita- 

 min qualitatively, and it is not surprising that in the years which 

 have been so largely spent in demonstrating the actual existence of 

 vitamins and learning something of their occurrence in plant and 

 animal organisms, the majority of investigators should have felt it 

 more interesting to survey the general field qualitatively than to 

 spend the large amount of time and labor necessary to make quanti- 



