PREFACE vii 



required an animal or a plant for its production. If this is lost sight 

 of amidst the overwhelming mass of material accumulated by the 

 great army of workers in the field of Carbon Chemistry if we have 

 produced thousands of compounds which do not and probably never 

 will be found to exist in living organisms ; if we have gone so far 

 beyond Nature as to make it appear unimportant whether an organic 

 compound is producible by vital chemistry or not, we are running the 

 risk of blockading whole regions of undiscovered modes of chemical 

 action by falling into the belief that known laboratory methods are 

 the equivalents of unknown vital methods. 



The whole contents of this work will show how little warrant there 

 is for assuming such an attitude as the above. Rather than interpose 

 such a barrier to future investigation it would be better to return to 

 the initial position and to ask critically how far chemical synthesis 

 has as yet thrown light on the physiological processes of animals and 

 plants. It is evident that no synthetical process of a pyrogenic 

 character is of any particular biochemical interest. The fundamental 

 synthesis par excellence the photosynthesis which plants are enabled 

 to accomplish, and in the course of which carbon dioxide is absorbed 

 by an organic compound and the product or products decomposed with 

 the liberation of oxygen is as yet without a laboratory parallel. It 

 has also long been recognised that many hydrolytic decompositions in 

 the living organism which result in the formation of definite products 

 are due to enzyme action. Such actions can generally be imitated by 

 laboratory methods, but the analogy between the natural and the 

 laboratory process disappears when it is considered that as yet no 

 organic nitrogenous hydrolysing agent of the nature of an enzyme 

 has ever been synthesised. 



Still more recently has it been shown to be probable that certain 

 up-grade syntheses in the living organism, i. e. the coalescence of 

 simpler to more complex molecules, may also be the result of enzyme 

 action *. Here again it may be said that the process might be imitated 

 by the use of chemical reagents, but the actual vital method has not 

 been reproduced in the laboratory. In emphasising these differences 

 between laboratory synthesis and synthesis in the living organism it 

 has appeared to me that some further stimulus might be given to bio- 

 chemical investigation, and this consideration has had much weight in 



1 Croft Hill, Trans. Ch. Soc., 1898, 73, 634 ; Ber. Deutsch. ch. Gesell. 1901, 34, 1380 ; 

 Kastle and Loevenhart, Am. Ch. Journ. 1901, 26, 533 ; Hanriot, Comp. Rend. 1901, 132, 

 212; Emmerling, Ber. Deutsch. ch. Gesell. 1901, 34, 3810; Fischer and E. F. Arm- 

 strong, Sitzungsber. Pr. Akad. Berlin, 1901, 123 ; Ber. Deutsch. ch. Gesell. 1902, 

 35, 3144. 



