PRESIDENTIAL ADDRESS. 443 
approaching very closely toa time when it should be possible to discuss such 
properties with considerable confidence. 
Still it must not be forgotten that the problems they offer are all valency 
problems and that the nature of valency eludes us entirely at present. 
The greatest advance which chemists may pride themselves upon having 
made during the past decade or two remains to be considered. In 1885, I 
spoke as follows :—‘ The attention paid to the study of carbon compounds 
may be more than justified both by reference to the results obtained and to 
the nature of the work before us ; the inorganic kingdom refuses any longer 
to yield up her secrets—new elements—except after severe compulsion ; the 
organic kingdom, both animal and vegetable, stands ever ready before us. 
Little wonder, then, if problems directly bearing upon life prove the more 
attractive to the living. The physiologist complains that probably 95 per 
cent. of the solid matters of living structures are pure unknowns to us and 
that the fundamental chemical changes which occur during life are entirely 
enshrouded in mystery. It is in order that this may no longer be the case 
that the study of carbon compounds is being so vigorously prosecuted. Our 
weapons—the knowledge of synthetical processes and of chemical function— 
are now rapidly being sharpened, but we are yet far from ready for the 
attack.’ 
My forecast has been more than justified ; indeed, the advance to be 
recorded is nothing short of marvellous: the great problems of vital 
chemistry appear now no longer to be unattainable to our intelligence— 
their cryptic character seems to have disappeared almost suddenly. Many 
have contributed in greater or less degree but none in such measure as Emil 
Fischer, whose work both in the sugar group and in connexion with the 
albuminoids must for ever rank as monumental. ; 
It is difficult to appreciate the extent to which the practical genius of 
this chemist has carried us—difficult alike for those who understand the 
subject and those who do not; the significance of his labours is only 
apparent when the bearing of his results on the interpretation of vital 
phenomena is fully considered. In 1885, we were disputing as to the 
structure of substances such as glucose and galactose; now we not only are 
satisfied that they belong to the group of aldhexoses (aldoses) derived from 
normal hexane but, taking into account the monumental discoveries of 
Pasteur to which precision has been given by van’t Hoff’s great generali- 
sation, we are in a position to assign fully resolved structural formule not 
only to the natural products but to the nine other isomeric aldhexoses which 
Fischer has prepared artificially. 
It is a striking fact that only three of the sixteen possible aldhexoses 
and but a single ketohexose (fructose), of which many are possible, are met 
with naturally. Nature is clearly most sparing, most economical, in her 
use of materials. And not only is this true of the hexoses, as very few of 
the possible lower and higher homologous carbohydrates occur in vegetable 
or animal materials and the condensed carbohydrates (cane sugar, starch, 
etc.) are all formed apparently from the hexoses and pentoses which occur 
naturally. The albuminoids, the alkaloids, the terpenes are also optically 
active substances ; in other words, only a limited number of the possible 
forms are present. There is reason to suppose that the compounds of 
natural occurrence stand in close genetic connexion and belong with few 
exceptions to the same series of enantiomorphs; in no other way is it 
possible to account for the occurrence of one only of the pair of enantio- 
morphous isomerides and for the relatively small number of compounds. 
Moreover, not only the sugars and most of the other products of the dis- 
integration of the albuminoids but also the amino-acids, in like manner, 
are derivatives of compounds containing at most six atoms of carbon ; the 
fats alone are of a considerably higher degree of complexity but they are 
probably collocations of the simpler units. 
