A TTEMPTS TO ISO LA TE PURE ENZ YATES. 3 1 3 
unorganised ferments are typically found in the secretions of specialised 
cells of the higher plants and animals, and take an important part in 
the chemical changes involved in their nutrition. 
There is probably at bottom very little difference in the manner of action 
of cellular ferments and enzymes. From the cell substances of several 
bacteria, extracts have been obtained possessing the same fermentative action 
as the living bacteria ; this indicates that in such bacteria, substances are 
present in the cell which act like ordinary unorganised ferments, but normally 
remain during the life of the cell within its substance, and perform their 
fermentative functions there. 
A good example of such an isolation of an unorganised from an organised 
ferment, is afforded by that series of brilliant researches into the nature of 
the action of the micro-organism, torula urese, upon urine, which began with 
the observation that the change into ammonium carbonate was not stopped by 
the presence of carbolic acid in sufficient amount to paralyse the growth of 
the micro-organism, 1 and ended in the extraction from the bacteria of 
a soluble ferment, which converted urea into ammonia and carbonic acid, even 
in the presence of chloroform, which effectually stops all bacterial action. 2 
In a similar manner, a soluble ferment, capable of inverting cane sugar, 
can be extracted from yeast cells after they have been killed by the action of 
alcohol or ether, 3 and from certain putrefactive bacteria unorganised ferments 
have been obtained, possessing an action on proteids analogous to that of the 
proteolytic ferment of the pancreatic juice. Such intracellular soluble ferments 
have not been shown to exist in by far the greater number of organised ferments, 
but if they do so exist the only remaining difference betAveen organised and 
unorganised ferments is that in the former the substance formed by the cell 
remains in the cell substance, and does its work there, the products of its 
action being poured forth as a kind of secretion or excretion, while in the 
latter the ferment becomes separated from the cell in a secretion, and carries 
out its work apart from the cell. 
Most of the chemical changes involved in the digestion of the food 
are brought about by the presence in the digestive secretions of soluble 
ferments. So that digestion might be described as the physical and chemical 
alteration of the foodstuffs, into forms better fitted for absoiytion, by the 
action of certain soluble ferments, tin: digest ire enzymes. 
Attempts to isolate pure enzymes. — Many attempts have been 
made to isolate chemically pure enzymes, but the task is very difficult, 
and it is highly probable that no one has yet succeeded in obtaining a 
pure product. 
There are two great difficulties in the way : first, our ignorance of a 
specific precipitant for any of the enzymes ; and, secondly, the extremely 
small quantities in which they are present in the secretions. On account 
of the first, the enzyme cannot be thrown out of solution unaccompanied 
by other substances ; on account of the second, it is not present in 
workable quantity, and is rapidly lost in any lengthened process of 
chemical manipulation. When to these disadvantages are added the 
non-diffusibility of the enzymes, which shuts out a means of separating 
them from the traces of proteid which always accompany them, and 
their sensitiveness to reaction and temperature, some idea is obtained of 
the difficulties which the problem of isolation presents. 
1 Hoppe-Seyler, Med.-chem. Untcrsuch., Berlin, 1871, Heft 4, S. 570. 
- Sheridan Lea, Journ. Physiol., Cambridge and London, 1885, vol. vi. p. 136. 
3 Hoppe-Seyler, Ber. d. dcutsch. chem. GeseUsch., Berlin, 1871, S. 810. 
