G.
WILLIAMSON
63
symbiotic micro-organisms which themselves are
closely associated with the food. Thus the nature
and number of cellulose-splitting organisms found
in the intestine at any given time depends upon
the extent to which plant food has formed part of
the diet previously, and the extent of their action
in a large measure depends upon the facilities
offered for their contact with the food over a pro-
longed period such as occurs in the rumen of cattle
and in the cæcum and colon of the horse. If the
cellulose is encrusted with such material as lignin,
cutin, silica, etc. their insoluble nature prevents
the action of either digestive juices or bacteria,
making the digestion of cellulose impossible and
denies, even to the ruminant, the use of the other
nutrients contained in it.
One of the features of the ageing of all grasses is
the proportionate increase in cellulose, and in the
lignification of its cellulose characterized by the
rigidity and brittleness of its stem, so that as the
plant gains maturity the amount of lignocellulose
composing it rapidly multiplies. The cereal
grasses are no exception to the rule, and as it is so
important in the harvesting of the grain that there
hould be tno lodging of the plants, those varieties
having straw of a stiff nature which can thus with-
stand rough weather conditions are favoured in
most districts. By far the commonest factor
governing the amount of lignification of straw,
however, is the stage at which the crop is cut. In
the straw of the unripe oat, for instance, the crude-
fibre content may be as low as 29.5 per cent or
even lower, but when the same straw has been cut
in a completely matured condition the fibre may
have almost doubled in amount and the lignin,
which in the former condition may have been al-
most absent, will in the latter case be present in
large amounts. The shorter the period of growth
the less will the process of lignification have pro-
ceeded. Of cereals, only oats are habitually cut in
the unripe state, and it is for this reason that oat
straw can without treatment form a useful food
even for horses. On analysis, barley straw may
appear to be superior to oat straw, but it is less
palatable; wheat straw and rye straw are very
much inferior and are useless as a food for horses—
in fact, as is well known, the horse may expend
more energy in dealing with such straw than is
supplied by the nutrients absorbed from it.
Their inferiority is almost entirely due to the
indigestible nature of their carbohydrates.
Knowledge is still lacking as regards the exact
nature of the a sociation of lignin and cellulose.
By some it is held to be a loose chemical combina-
tion ; by others the relationship is considered to be
a very close chemical one. The latter view is to-
day more widely held than the former. Nearly all
authorities are agreed that a characteristic of
lignin is the presence of methoxy and acetyl groups
in its molecule, and it is known that these are
easily split off by the action of heat and alkali and
that if the process is repeated sufficiently often at
high enough temperatures the lignin can be com-
pletely removed. Lignin and ligno-cellulose, the
term used to denote the connection between the
two substances, are quite indigestible, for they are
acted upon neither by the digestive juices nor by
the intestinal micro-organisms. It has been
suggested and it can quite readily be understood
that the indigestibility of fibre may not be so much
dependent upon the amount of lignin which it may
contain as the manner of the disposition of the
lignin within the cell wall. The presence of but
a small amount of lignin may or may not be res-
ponsible for a pronounced lowering of the digesti-
bility of the fibre of a crop, depending on whether
the lignin is distributed in a thin impervious layer
locking up the otherwise digestible material or
whether, on the other hand, the lignin is less evenly
distributed and a certain amount of the fibre cells
are free for digestion.
The common farm process which has been
practised for generations of chopping, grinding or
fermenting straw does only to a slight extent in-
crease its digestibility. The chopping or grinding
saves the expenditure of energy and to that extent
enhances the feeding value of the material, the
fermentation increases the palatability, but grind-
ing may actually decrease it. What might be
considered an extension of these processes carri-
ed out on a commercial scale has been tried in
several countries. The best known one in this
country was that carried out by the d'Orby Pulp &
Fodder Company whereby the material was
exposed to steam under pressure, dried and ground
to a meal. The principle of a process used by
Price in Australia was similar, while modifications
of the same process were tried out in Germany
and Russia. One may say, however, that, while
palatability was greatly increased, in each case the
food value of the straw was not sufficiently raised
to make the process of much practical value.
Some fifty years ago Lehmann demonstrated
that the nutritive value of straw could be enhanced
by the act on of hot alkali, and shortly afterwards
Kellner showed that straw treated for the manu-
facture of paper by hot soda solution under pres-
sure greatly increased its value as a food. Con-
firmatory tests in later years showed that anything
up to 100 per cent of the cellulose freed from in-
crusting substances in this manner was digested
by ruminants. Although straw was little used in
Britain for paper-making it was always used
extensively for that purpose on the Continent.
When the process employed in paper manufac-
ture was simplified to bring it within the range of
ordinary farm practice, it was shown that the
difficulties were great and the disadvantages very