the surface of the butter and the edge of the vessel should be
filled with fine dry salt, instead of pickle. A common mistake made is
the holding over for too long a time of the butter: the sooner this
article can be disposed of the better, for _it never improves by age_.

* * * * *

[Footnote 23: From two Greek words, signifying odour and soup.]

[Footnote 24: "A New Inquiry, fully illustrated by coloured engravings
of the heart, lungs, &c., of the Diseased Prize Cattle lately exhibited
at the Smithfield Cattle Club, 1857." By Frederick James Gant, M.R.C.S.
London, 1858.]

[Footnote 25: Professor John Wilson's Report of the Agricultural
Exhibition, Aarhuus, 1867.]

PART V.

ON THE COMPOSITION AND NUTRITIVE VALUE OF VEGETABLE FOODS.

SECTION I.

THE MONEY VALUE OF FOOD SUBSTANCES.

The flesh-forming principles of food are, as I have already stated,
almost identical with the principal nitrogenous constituents of animals.
Unlike the non-plastic substances, they are convertible into each other
with little, if any, loss either of matter or of force. Not many
years since it was the fashion to estimate the nutritive value of a
food-substance by its proportion of nitrogen; but this method--not yet
quite abandoned--was based on erroneous views, and yielded results very
far from the truth. No doubt all the more concentrated and valuable
kinds of food are rich in nitrogenous principles; but there are other
varieties, the nutritive value of which is very low, and yet their
proportion of nitrogen is very high. This point requires explanation.
Both the plastic and the non-plastic materials of food exist in two
distinct states--in one of which they are easily digestible, and in the
other either altogether unassimilable or so nearly so as to be almost
useless. Thus, for example, the cellular tissue of plants, when newly
formed, is to a great extent digestible, whilst the old woody fibre is
nearly, if not quite, incapable of assimilation. Gelatine, which in raw
bones is easily digested in the stomachs of the carnivora, loses a large
proportion of its nutritive value on being subjected to the action of
steam. Again, a portion of the nitrogen of young succulent plants is in
a form not sufficiently organic to admit of its being assimilated to
the animal body. But, independently of these strong objections to the
method of estimating the nutritive value of food by its per-centage of
flesh-f