322 
the other carbon compounds and to the in- 
vestigation of the nitrogenous substances, 
as yet scarcely well begun. These may be 
expected to put physiologists into possession 
of valuable clues to the secrets of nutrition 
and respiration. 
How intimate this relation between the 
arrangement of atoms in space and physio- 
logical activity is, is to be seen in the fact 
that fermentability is dependent upon the 
configuration of the sugar molecule. It has 
been found that, of the many sugars known, 
only those with 3, 6, or 9 atoms of carbon 
in the molecules are fermentable. Thus 
the triose sugar, glycerose, whose formula 
is C,H,O,, is fermentable, while the tetrose 
sugar, erythrose, C,H,O,, and the pentoses, 
ribose, lyxose, xylose, and arabinose, 
C,H,,0,, are not. In like manner several 
of the hexoses, C,H,,0,, and the nonnoses, 
C,H,,0,, are fermentable, while the inter- 
mediate ones, such as the heptoses, C,H,,0,, 
are not. 
But the relation is yet more intimate. 
Even when the proper number of atoms is 
present they may be arranged in such a 
fashion as not to be open to disturbance by 
an organism. 
Thus, certain species of yeast are capable 
of fermenting d-glucose, d-mannose, and 
d-galactose. The arrangement of their 
molecules may be represented in a plane as 
follows : 
H H OH H 
d-glucose = CH,OH—C—C—C—C—COH 
OH OH H OH 
H H OH OH 
d-mannose = CH,OH—C—C—C—C—COH 
OH OH H H 
H OH OH H 
d-galactose =CH,OH—C—C—C—C—COH 
OH H H OH 
But d-talose, whose structure is the fol- 
lowing : 
SCIENCE. 
[N. 8. Von. X. No. 245. 
H OH OH OH 
CH,OH—C—C—C—C—COH 
@Jsl Jel isl) Jet 
cannot be fermented by these yeasts. In- 
spection shows that d-talose differs from 
d-galactose and d-mannose only in the 
transposition of the molecular groups about 
a single one of the asymmetric carbon 
atoms, and from d-glucose only in the 
transposition about two carbon atoms. 
Again, while d-glucose, 
H H OHH 
CH,OH—C—C—C—C—COH, 
OH OH H OH 
is fermentable, its isomer, /-galactose 
OH OH H OH 
CH,OH—C—_C—_C—C_—COH, 
H H OHH 
is not at all fermentable. 
The discovery that yeasts, long believed 
to show direct ferment action of the pro- 
toplasm, produce the chemical changes 
known as fermentation by the intervention 
of enzymes, removes the problem from the 
immediate field of physiology, only to group 
it with the host of baffling catalytic phe- 
nomena which the chemist is at present’ 
wholly unable to explain. Thus all fermen- 
tations at present known become closely 
associated with the digestive processes in 
nutrition. We may scarcely expect light 
upon all these phenomena until the prepa- 
ration of the enzymes in a state of purity is 
attained. This, it is to be hoped, will be © 
followed by a knowledge of their com- 
position, though, as they now appear to be- 
long to the group of nucleo-proteids, this 
may only he ascertained when the long- 
awaited desideratum is attained and we 
know the composition of proteids them- 
selves. 
The action of the enzymes, which is lim- 
ited by the molecular constitution of the 
substances they hydrolyze and break up, is 
