360 CARNEGIE INSTITUTION OF WASHINGTON. 



nitrogen of unknown character are also introduced into the diet. 

 There is therefore a question whether or not this nitrogen does not in 

 fact supplement deficiencies in the protein. If, however, a preparation 

 of vitamine could be obtained which was so potent that very small 

 quantities were enough to meet the animal's requirement the amount 

 of nitrogen and other substances thus introduced might be so small as to 

 render objections of the above sort of little force. 



We have accordingly devoted much time to attempts to prepare 

 such a product from yeast and are now in possession of a relatively 

 large amount of material which, according to the trials thus far made 

 with it, appears nearly if not quite as efficient in supplying the water- 

 soluble vitamine as was the yeast itself from which it was obtained. 

 Thus daily doses of 16 milligrams of this product have proved about 

 as effective in restoring rats which have declined on a diet free from 

 water-soluble vitamine as have doses of 200 milligrams of the original 

 dried yeast. Such a quantity of dried yeast appears to be in general 

 about the minimum which can be depended on promptly to bring 

 declining rats back to normal. 



Although it is improbable that all of the water-soluble vitamine of 

 the yeast is concentrated in the material now on hand, this product is 

 far more potent than any we have heretofore had at our command. 

 This fraction contains only 7.5 per cent of nitrogen, hence only 1.2 

 milligrams of nitrogen are added to the daily diets of 5 to 10 grams of 

 our foods rich in fat. Such a quantity can scarcely be expected to 

 affect the nutritive value of the protein in such foods. Thus, if the food 

 intake of a very young rat is 5 grams per day and this contains 10 per 

 cent of protein, its nitrogen content is 80 milligrams. The 1.2 milli- 

 grams of nitrogen added with the vitamine is, therefore, less than 1.5 

 per cent of the total nitrogen of the food. With increasing food intake 

 the added nitrogen forms a correspondingly smaller proportion. It is 

 probable that we shall soon learn to concentrate the vitamine still 

 further and thereby correspondingly reduce the uncertainties w^hich 

 have heretofore pertained to some of our experiments. 



We also hope to chemically define the water-soluble vitamine still 

 more narrowly by excluding various groups of substances whose 

 absence from the effective fraction can be demonstrated. Some groups 

 have already been excluded, and it is confidently expected that others 

 may soon be added to this list. In this way it ought to be possible to 

 simplify the problem of ultimately establishing the chemical identity 

 of this mysterious food factor. Some light may also be gained on the 

 question of whether what is now termed the water-soluble vitamine is 

 a single substance or a mixture of two or more, as our experiments with 

 wheat embryo suggest. As we have only recently been able to prepare 

 a sufficient supply of this yeast fraction, its chemical examination has 

 just been begun. 



