176 THE VITAMINS 



40 grams of fresh yeast, and 75 grams of egg yolk emulsified with 125 

 cubic centimeters of water. On this, guinea pigs are said to succumb 

 to scurvy without exception before the thirty-third day unless the diet 

 is supplemented with an antiscorbutic, 3 cubic centimeters of lemon 

 juice daily being the minimum protective dose for a 400 gram animal. 



Eddy (1929) modified the Sherman-La Mer-Campbell basal ration 

 by substituting 1 per cent of cod-Hver oil for the equivalent amount of 

 butter fat in order to insure against vitamin D deficiency and by feeding 

 yeast separately as an additional source of the vitamin B complex. 



Along with lack of uniformity in the basal diets are corresponding 

 variations in methods of recording results. One basis for the expression 

 of the relative antiscorbutic value of foods is the "minimum protective 

 dose" which represents the daily allowance of the food in question 

 which just meets the need of the guinea pig for complete protection 

 from scurvy. Another way is to express the antiscorbutic value of the 

 food in comparison with that of some well-known antiscorbutic such as 

 orange juice, which for convenience of comparison may be given an 

 arbitrary value of 100. 



The unit method of calculating vitamin values as described for 

 vitamin B (Ch. II) affords perhaps the most convenient mode of ex- 

 pression. The unit of vitamin C suggested is that amount which when 

 fed as a daily allowance just suffices to afford complete protection from 

 scurvy (as the term is here used) to a standard guinea pig as described 

 in the method for quantitative determination of vitamin C above de- 

 scribed. This is essentially what was proposed by Chick and Hume who 

 called it the minimum protective dose (m.p.d.). 



The use of scurvy scores to form a judgment of the fraction of 

 complete protection an animal has received and from this to calculate 

 the amount required for complete protection should be attempted only 

 by skilled and experienced observers, but in such hands it has the 

 advantage of bringing into the quantitative interpretation a larger 

 proportion of the test animals than simply those which received exactly 

 the minimum protective dose. 



Bezssonoff (1921b, 1923a) claimed to have discovered a color test 

 for vitamin C sufficiently specific to be of value as a substitute for the 

 feeding method. The reagent is essentially the Folin-Denis phenol 

 reagent modified by reducing the proportion of concentrated phos- 

 phoric acid to one-third the original amount and adding without 

 heating an equal volume of normal acid (sulfuric, hydrochloric, or 

 nitric). This was said to give a slate gray color turning to blue with 

 various extracts of known antiscorbutic properties but not with the 



