Preface to Second Edition 



Few groups of substances can rival the vitamins in the extent of the 

 development of knowledge regarding their scientific significance in ad- 

 vance of the working out of their structural formulas. 



In the pages which follow, an attempt has been made to summarize 

 the very considerable amount of information which has been gained 

 regarding the chemical natures of the individual vitamins, and the more 

 voluminous knowledge regarding their roles in life processes, their for- 

 mation and distribution in nature, their relative abundance in dififerent 

 types of food materials and stability under the conditions to which 

 these are likely to be subjected. 



It is doubtless only because the history of the discovery of the vita- 

 mins and of the recognition of their great scientific and practical im- 

 portance has been made so rapidly as to outrun the investigation of 

 their chemical natures, that the chemically very dififerent substances 

 here considered are grouped together under one collective designation. 

 With increasing knowledge it becomes more and more evident that 

 several (at least) of the vitamins are of very different chemical nature 

 from each other. The trend of the findings of recent research is de- 

 cidedly toward diversification rather than unification of the chemistry 

 of the vitamins. The time is already past for any such unified style of 

 treatment as would be suggested by the literal interpretation of the 

 term monograph : to attempt it would not be consistent with present 

 knowledge of the wide chemical differences between individual vitamins. 



Hence we have attempted rather to summarize the more important 

 of our knowledge of each vitamin in a separate chapter, letting each 

 chapter develop into the form best suited to the presentation of its 

 own subject-matter, and to append a collective bibliography sufficiently 

 complete to guide the reader to practically all the important literature 

 of the vitamins. 



In general both the text and the bibliography have been brought 

 down to about the middle of the year 1930 ; but our endeavor has been 

 to serve the reader as effectively as circumstances would permit rather 

 than to maintain a meticulously uniform date-limit, and it will doubt- 

 less be found that contributions near at hand have been included down 

 to a somewhat more recent date than those published at a great distance 

 or for other reasons less readily accessible. 



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