meat extract." Yeast extracts contain purin bodies, and are probably
equally as injurious as meat extracts. Such strong and rank flavours (the
odour is suggestive to us of putrefaction) should be discouraged by those
who would cultivate a refined taste in food.

Flesh Bases and Waste Products.--As the result of destructive
metamorphosis or the wearing out of the body, there remain certain waste
products which have to be expelled as soon as is possible. Their retention
and accumulation would soon produce death. A part is expelled by the
lungs as carbon-dioxide, or as it is generally though less correctly
termed, carbonic acid. Upon the breaking down of the complex proteid and
other nitrogenous matter, the nitrogen is left in comparatively simple
combinations. These effete nitrogen compounds are commonly termed flesh
bases or nitrogenous extractives. They exist in small quantity in flesh
meat, but are concentrated and conserved in the making of beef-tea or
beef-extract. The spleen, lymphatic and other glands, and especially the
liver, break these down into still simpler compounds, so that the kidneys
may readily separate them from the blood, that they may pass out of the
body. By far the largest part of this waste nitrogen is expelled from the
bodies of men and many other mammals in the form of urea. Pure urea is an
odourless transparent crystalline substance, of cooling saline taste like
nitre. It is soluble in an equal volume of water, and is expelled from the
body with great ease. In the herbivora the nitrogenous waste takes the
form of another body called hippuric acid. The nearly solid light-coloured
urinary excretion of birds and serpents consists of urates; this is uric
acid in combination with alkalies. In man, in addition to the urea
excreted, there is also a little hippuric and uric acid or compounds of
these. Uric acid is a transparent colourless crystalline body almost
insoluble in water but soluble as urates in the presence of alkalies. As
deposited from urine it is of a dull red sand-like appearance, as it has a