a. The stimulants.

b. The depressants.

Those which stimulate the central nervous system are: caffeine, strychnine, atropine, and cocaine.

Central Nervous Stimulants The Caffeine Group

This includes the three alkaloids, caffeine, theobromine, and theophylline, caffeine being chemically a trimethyl xanthine, and the other two, dimethyl xanthines. They are purin bodies, are closely related to uric acid, and are but feebly basic, i. e., have little power to form salts.

There are three classes of purins:

1. The oxypurins, which include hypoxanthine, xanthine, and uric acid (trioxypurin or oxyxanthine).

2. The aminopurins, which include adenin and guanin.

3. The methyloxypurins, which include this caffeine group.

Remedies Whose Chief Action Is Upon The Central Ne 45

Purin, C8H4N4

Remedies Whose Chief Action Is Upon The Central Ne 46

Xanthine, C5H4N4O2

Remedies Whose Chief Action Is Upon The Central Ne 47

Theobromine.

Remedies Whose Chief Action Is Upon The Central Ne 48

Uric acid, C5H4N4O3

Remedies Whose Chief Action Is Upon The Central Ne 49

Caffeine, trimethyl xanthine.

Remedies Whose Chief Action Is Upon The Central Ne 50

Theophylline.

By these formulae the purin nature of the drugs of this group is evident, as also their close relation to uric acid.