at Home and Abroad. 
241 
eminent colleague, Dr. Voelcker, would have written a separate 
paper on this subject in elucidation of the facts contained in 
this Report if his health had permitted. All I can do, there- 
fore, is to give a very broad statement of the questions involved, 
as I understand them, subject to Dr. Voelcker's correction on a 
future occasion. The chemical changes which fodder under- 
goes in silos have not jet been thoroughly investigated, but 
they may be indicated by one word — fermentation. The theory 
of fermentation, also, is by no means the least debateable in 
the range of chemical science ; but it is generally understood to 
practically resolve itself into the conversion of sugar, gum, 
starch, or allied compounds into simpler bodies, such as carbonic- 
acid gas, lactic acid, alcohol, acetic acid, &c. 
The various kinds of fermentation have been shown to be due 
to the action of innumerable minute microscopic organisms, the 
germs of which are freely distributed in the atmosphere. These 
organisms live upon fermentable substances, and transform 
them into simpler compounds, much as the animal transforms 
the food it consumes and the air it breathes into carbonic acid, 
urea, and other bodies. Each special kind of fermentation is 
said to be produced by a more or less distinct class of organism, 
and the precise nature of the fermentation set up may therefore 
be inferred to depend upon what particular species of organism 
is most favoured by the nature of the fermentable substance and 
the conditions in which it is placed. In most cases the changes 
involved in fermentation take place only in the presence of 
some nitrogenous substance, which, under the vital action of 
the organisms, becomes partly converted into a chemical 
" ferment," and in the presence of a sufficient quantity of water. 
But the special nature of the fermentation set up depends upon 
a multitude of circumstances ; and in the case of fodder in silos 
probably to some extent upon the proportion of sugar contained 
in the plant. For example, green maize generally contains a 
large quantity of sugar in comparison with other fodder-crops, 
and is said to undergo lactic fermentation. Without entering 
into details, this means that it becomes a kind of sauer-kraut or 
pickle, without passing through any intermediate stage of fer- 
mentation, and therefore with the minimum amount of loss of 
nutritive material. 
But it is rarely the case that our English fodder crops 
contain a sufficiently large proportion of sugar to enter largely 
into lactic fermentation. Therefore, as soon as fermentation 
begins, alcohol is formed. This means a certain loss of nu- 
tritive matter, which is carried still further by the almost im- 
mediate conversion of the alcohol into aldehyd — a very evanescent 
substance which, with the fodder itself, produces the smell so 
VOL. XX. — S. S. R 
