itute the _vegetable bases_; while those
of the second type are the _proteins_.

The vegetable bases may be divided into three groups. These are (_a_) the
_plant amines_, which are simple open-chain amines; (_b_) the _alkaloids_,
which are comparatively simple closed-ring amines, containing only one
nitrogen atom in any single ring; and (_c_) the _purine bases_, which are
complex compounds containing a nucleus with four carbon atoms and four
nitrogen atoms arranged alternately to form a double-ring group.

THE PLANT AMINES

The simple amines bear the relation to ammonia, or ammonium hydroxide,
represented by the following formulas, in which the R indicates any simple
alkyl radical:

H R R R R R H H
/ / / / \ / \ /
N-H N-H N-H N-R N-R N-H
\ \ \ \ / \ / \
H H R R R OH H OH

Ammonia Primary Secondary Tertiary Quaternary Ammonium
amine amine amine amine hydroxide

The simple amines which occur in animal tissues are known as "ptomaines"
and "leucomaines." The ptomaines are all decomposition products resulting
from the putrefactive decay of proteins caused by moulds or bacteria. Some
of these are highly toxic, producing the so-called "ptomaine-poisoning";
while others are wholly innocuous. They are all simple amines. Putrescine,
di-amino butane, NH_{2}.CH_{2}.CH_{2}.CH_{2}.CH_{2}.NH_{2}, and cadaverine,
di-amino pentane, HN_{2}.(CH_{2})_{5}.NH_{2}, are common non-toxic
ptomaines, resulting from the decay of meat. Neurine, trimethyl-ethylene
ammonium hydroxide, (CH_{3})_{3}(C_{2}H_{3}).NOH, is a violently poisonous
ptomaine produced in the decay of fish. Amines of similar structure to
these are occasionally found in living animal tissues. Such compounds are
known as _leucomaines_, to distinguish them from the _ptomaines_, which are
found only in dead material.

Corresponding in structure and properties to these amines of animal origin,
there is a series of basic substances, found in many plants, known as the
_plant amines_. The following are common examples:

=Trimethyl amine=, (CH_{3})_{3}N, is a very volatile compound, found in the
flowers of several species of the Rose family, the lea