688 
chemical change in disproportionately large 
quantities of material. When the newly 
produced substances attain a certain con- 
centration the further action of the enzyme 
is inhibited, but its action is reasserted 
when the concentration of the zymolytic 
products is again lowered. Maximum, 
minimum and optimum temperature and 
pressure influence these changes. The in- 
troduction of certain chemical bodies also 
exerts an accelerating or retarding influ- 
ence; and phenomena of selective action are 
likewise to be found. 
Many hypotheses have been submitted. 
Very ingenious explanations of some of 
the phases of fermentation are to be found 
in them ; but under the searching light of 
completer knowledge their incompleteness 
is sooner or later developed. Many of the 
modern theories are little else than trans- 
lations of the earlier hypotheses into terms 
of modern scientific terminology, so that 
the later literature is laden with modern 
extensions of the catalytic theory of Ber- 
zelius, Beal’s bioplastic theory, Justus von 
Liebig’s physical theory, the germ theory, 
etc. 
Interesting and enlightening as some of 
these theories are, their full consideration is 
not within the purpose of this address, the 
limits of which will permit only a brief 
and incomplete review of some of the more 
modern conceptions of fermentation, to 
which attention is now asked. 
The more recent investigations of the 
organized and unorganized (soluble) fer- 
ments have dealt a severe blow to the vital- 
istic theory of fermentation. Hansen’s ad- 
mirable biological researches upon the 
yeasts, followed by the important inves- 
tigations of Buchner, A. Croft Hill, Emil 
Fischer and many others brought to light 
many interesting hitherto hidden facts ; 
and it now seems clear that all the phe- 
nomena of fermentation may be explained 
from a purely chemical basis. The so- 
SCIENCE. 
[N. 8S. Von. XIII. No. 331. 
called organized ferments appear to be 
‘active proteids,’ and the unorganized fer- 
ments, or enzymes are mostly proteid-like 
bodies presenting great differences in the 
complexity of their chemical structure. 
Hueppe looks upon ‘active proteid’ as 
‘(a kind of intermediate stage between life- 
less ‘nutritional’ proteid and living cells”’; 
that it ‘appears like an anhydride of dead 
proteid,’ inasmuch as hydration converts it 
into an inactive form. Investigations of 
Bokorny and Loew demonstrated the ex- 
istence of active proteid in many plants. 
Loew speaks of it as reserve protein matter 
of a highly labile nature, and that it differs 
from all other reserve proteins. He called 
it proto-protein, and suggested that it is 
the ‘material which, by being converted 
into organized nucleo-proteids, forms living 
matter.’ Protein comprises all kinds of 
albuminous matter, while proteid is used 
to designate complex compounds of proteins, 
such as nucleins, hemoglobin, ete. Labile 
chemical compounds are unstable bodies 
which easily undergo chemical change. 
Labile atoms or groups of atoms are atoms 
or groups of atoms which readily migrate 
from a center of instability to one of sta- 
bility. When the migration is intramolec- 
ular a stereoisomeric compound is the prod- 
uct of change; when the migration is extra- 
or intermolecular disruption of the molecules 
takes place. Loew points out the necessity 
of distinguishing between ‘ potentially labile 
and kinetically labile compounds ; in other 
words, between static labile and dynamic 
labile ’—using the potential chemical energy 
in the sense of intramolecular chemical 
energy. Nitroglycerole and certain other 
explosive organic compounds represent the 
potential type, while examples of the ki- 
netic are found in the aldehydes and 
ketones. 
The energy stored ina labile compound 
is beautifully illustrated in the explosion of 
the trinitrate of glyceryl—CH,(ONO,).CH 
