374 
Micro-organisms and their Action 
humbly provide for contingencies, to remember that at present 
there are no exact rules of science under which he can conquer 
this dour earth of ours ; and costl v though it be, he must be 
content to do what, with no assurance of great reward, his ances- 
tors have done before him — adopt those measures which many 
failures and mucli painful experience have shown to be of most 
service in the particular spot on which he applies his energies 
and resources. 
Side bj side with social progress the ameliorating changes . 
have been advanced, not bj the silent operations and develop- 
ment of Nature or by the natural increment of value, but by the 
dogged effort which the landowner as a rule has ever put forth 
in the making of the land, and at any cost fitting it for the 
practice of improved husbandry suited to the progress of civili- 
zation and the modern wants of the people. 
X\'I. — Micro-organisms and their Action on Milk and Milk- 
Products. By Dr. P. ViETH, F.C.S., F.I.C. 
UXDEE the general term of " fermentation " are understood certain 
changes and decompositions of organic substances. However 
different in their ultimate results they may be, all kinds of fer- 
mentation have one thing in common by which they are distin- 
guished from processes, otherwise of a similar nature, viz. that 
very small quantities of the active agent (the ferment) which 
causes a particular kind of fermentation, are able to trans- 
form or decompose proportionately large quantities of the 
fermentable substance. 
According to the nature of the ferment, the many different 
kinds of fermentation can be classed into two groups, viz. 
fermentations which are caused (1) by chemical ferments or 
Enzymes, and (2) by organized ferments. 
Enzymes are ?/72organized compounds, which are soluble in 
water. It is most difficult to prepare them in a perfectly pure 
state, hence very little is definitely known with regard to their 
chemical composition and constitution. Although enzymes 
are capable of effectively attacking and changing a very great 
multiple of their own quantity of the fermentable substance, it 
appears that during their action they are undergoing certain 
changes themselves, by which their efhciencv is completely 
neutralized. By heating aqueous solutions of chemical fer- 
ments, the latter are rendered ineffective at a temperature much 
below boiling-point, viz. at about 170" Fahr. Instances of 
