president’s address. 
293 
1837 were found to possess the property of producing prussic 
acid, sugar, and an aldehyde when macerated with water. 
This property was found to be due to the interaction of two 
bodies, an enzyme (emulsin) and a glucoside (amygdahn), 
which can be isolated separately from the seeds and are 
capable of producing the same reaction in vitreo after 
separation in a more or less pure state from the plant tissues. 
This is one of the first instances of the discovery and pre- 
paration from vegetable material of an enzyme, and this 
particular case of the interaction of an enzyme and a gluco- 
side has been studied more than any other. Another well- 
known enzyme-glucoside couple occurs in black mustard 
seed, the enzyme being the characteristic enzyme of the 
cruciferse, myrosin. Here the product of the interaction in 
addition to sugar is not prussic acid, but the essential oil of 
mustard. 
On this analogy, therefore, it seems highly probable that 
in the case of linseed we have to deal with a case of inter- 
action between an enzyme and a glucoside. If so, we shall 
be able to prepare them separately from the plant tissues, 
and shall find that when so isolated they will interact exactly 
as they do when brought together by the solvent action of 
water in the macerated cellular tissue in which they have 
been elaborated. 
It is the enzyme which interests us mainly now, because 
its properties are of far-reaching importance and influence in 
the order of nature. The glucoside is a much more ordinary 
body, and is only one of the countless substances upon which 
enzymes exert their activity. Glucosides occur in nature in 
the leaves and seeds of plants and in the bark of trees, and 
are so called because when decomposed by mineral acids or in 
nature by the action of an enzyme the products are invariably 
a sugar, generally glucose, and another organic body the 
nature of which varies with the class of glucoside. At present, 
for instance, we are considering specially a class of glucoside 
