SYNTHETICAL CHEMISTRY 15 



us say, from carbon and hydrogen or from calcium carbide and water, 

 and every known organic compound. At present the two modes of 

 treatment have perforce been combined, and it must be left to the 

 judgement of chemists and physiologists respectively to attach the 

 proper weight to such data as they may gather from these pages for 

 the purposes 'of any particular inquiry. 



It may perhaps be considered presumptuous on the part of a writer 

 who lays no claim to be considered a physiologist to caution students 

 of this science that the work now offered does really contain in spirit, 

 if not in the text, the two distinct lines of treatment above indicated, 

 and that there is a danger in making too free use of laboratory rela- 

 tionships between organic compounds as evidence of physiological 

 relationship without direct physiological evidence in confirmation. 

 The extreme difficulty of obtaining such confirmation has already been 

 conceded ; nevertheless any chemist who considers some of the physio- 

 logical speculations which have been advanced of late years cannot 

 but come to the conclusion that genetic relationships established 

 experimentally by chemists have been overstrained in the service of 

 physiology. The ordinary chemical equation representing the genetic 

 relationship of one vital compound to another is apt to delude those 

 who are not experts in chemistry into the belief that it is all-sufficient 

 and that it ' explains ' the biochemical process : as a matter of fact the 

 sign connecting the two sides of the equation stands for the whole 

 unexplored region of biochemical transmutation. 



It may perhaps be urged as a countercharge against chemists that 

 many of the highest authorities have advanced purely chemical 

 explanations of biochemical transformations without sufficient physio- 

 logical evidence. This must be frankly admitted, but it may be 

 pleaded in excuse that the physiological evidence has not been avail- 

 able partly owing to the practical difficulties of obtaining it, and 

 partly owing to want of co-operation between the two departments of 

 science. Such speculative advances, however, if taken at their true 

 scientific value and not exalted to the rank of proved theories, can 

 do no harm, and may do much good in advancing biochemical science 

 by acting as suggestions stimulating further observation and experi- 

 ment in this all-important field. 



Not the least difficult task in connexion with the present compila- 

 tion has been the restriction of the series of intermediate compounds 

 within reasonable limits. Although much judgement has been exer- 

 cised, it may appear even now that many of the genetic relationships 

 are extremely far-fetched that the number of intermediate com- 

 pounds has been multiplied to an unnecessary extent, and that stages 

 have been interpolated which would certainly never be passed through 

 in the course of any practical series of laboratory operations for the 

 synthesis of one compound from another. Again, therefore, it may be 

 necessary to insist that this work is not a practical laboratory guide, 



