These substances in their chemical constitution lie between alcohols and acids. They are obtained from alcohols by the removal of two atoms of hydrogen, hence the name aldehyde (alcohol dehydrogenatum).

They contain the group salts in darkness. Living protoplasm has a similar power, whereas dead protoplasm has not, and from this circumstance it has been supposed that active albumin contains the aldehydic group in its constitution.

They reduce silver

(p. 22). They reduce silver

This supposition is supported by the fact that substances which act energetically upon aldehydes are also protoplasmic poisons.1

Acetic Aldehyde. - Synonyms: Aldehyde, ethyl aldehyde, or ethylidene oxide. C2H4O. Not officinal.

Characters. - A colourless, mobile liquid, with an ethereal, acrid, and suffocating odour. Specific gravity 0.79. Boiling-point, 22° C. (71°.6 F.).

Preparation. - It may be prepared in several ways, as the hydrogen can be removed from alcohol either by oxidising agents or chlorine. C2H6O + O = C2H4O + H2O, or C2H6O + Cl2 = C2H4O + 2HC1.

Action. - It is antiseptic. It has a strong local irritant action. When inhaled it causes excitement followed by anaesthesia. It has a powerfully depressant action on respiration, and rapidly produces asphyxia, so that it is not used as an anaesthetic.

Paraldehyde. C6H12O3. - It appears to be a polymeric modification of aldehyde. Not officinal.

1 O. Loew, Pfluger's Archiv, xxxv. p. 516.

Characters. - A colourless fluid.

Dose. - 3 to 6 gm., or more; 1/2 to 1 fl. drachm.

Administration. - It is soluble in about 8 parts of water, and may be given with glycerin, syrup of tolu, or syrup of oranges.

Action and Uses. - It is a pure narcotic, causing sleep like chloral. It is about half the strength of chloral, and is said to be without any depressing action on the heart and respiration. It may thus be used instead of chloral in cases of weak heart. Its local action renders its use unadvisable in severe gastric disorders and laryngeal phthisis.

Inconvenience. - It causes an unpleasant smell in the breath, which is very disagreeable to some patients.