16 INTRODUCTORY 



but that its object is to furnish material for evolutional schemes of 

 genetic relationships which are chemically real, however far-fetched 

 they may appear from a laboratory or technical point of view. 



Thus, to state the case in an abstract form, a vital product, X, is 

 capable of being produced from a certain generator, A, by the action 

 of heat or chemical reagents. But A by treatment with certain other 

 reagents can be transformed into the compounds P, Q, R, &c., each one 

 of which, or only the last one, say R, can by appropriate treatment be 

 converted into X. It may be urged against the system adopted in this 

 work that since X can be directly obtained from A , the intermediate 

 compounds P, Q, R, &c., have been interpolated unnecessarily. This 

 objection is valid from a practical point of view, but if the fact that X 

 is obtainable from P, Q, and R were for this reason omitted the genetic 

 relationships between A, P, Q, R, and X would be lost sight of. More- 

 over it is possible and in fact during the preparation of this work 

 numbers of actual cases have occurred that one or all of the inter- 

 mediate compounds P, Q, R may be at present, or may be found sub- 

 sequently to be, synthesisable from some generator other than A, let us 

 say B, so that B then becomes a generator of X a fact that would 

 have been ignored if P, Q, R had not been interpolated between A and 

 X. It is further possible that some natural source of one of the inter- 

 mediate compounds, say R, might be discovered hereafter, in which 

 case the genetic relationship of the vital product R to A at one end 

 and X at the other would then be deducible from this work. Provision 

 is accordingly made by this treatment not only for the possible 

 development of further chemical relationships through the discovery of 

 new modes of synthesising compounds which are now non-vital inter- 

 mediate stages, but likewise for the possibility of some non-vital pro- 

 ducts, at present only used as stepping-stones in the laboratory series 

 of operations, being hereafter found in nature. 



In illustration of the advantages of this system a system in which 

 directness and simplicity of transformation cannot be allowed to deter- 

 mine which synthetical processes shall be included and which excluded 

 the case of diacetyl [113] may be quoted. When the section dealing 

 with quinol [7l] was first written the generators of diacetyl had to be 

 included among the generators of this phenol. It was afterwards 

 found in the laboratory of Sohimmel & Co. that diacetyl is a consti- 

 tuent of certain ethereal oils, so that this compound, at first introduced 

 only on account of its genetic relationship to quinol, thereupon had to 

 be enrolled among the vital products and so, as it were, to have its 

 importance enhanced by having biochemical interest added to its 

 purely chemical interest as an indirect generator of quinol. Had 

 diacetyl been excluded because its connexion with quinol is only of 

 an indirect character an interesting relationship between two vital 

 products would have been lost sight of. The cases in which new 

 synthetical processes for the production of non-vital intermediate 



