This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
Cepa vulgaris C. B. Allium Cepa Linn. Onion: a plant with a single bulbous root composed of a number of coats; producing long fistular leaves, and a tall naked bellied stalk, bearing a large cluster of hexapetalous white flowers, each of which is followed by a roundish capsule, containing a number of black angular seeds. It is cultivated in gardens for culinary uses.
Onions are very acrid, stimulating, and of little nourishment. Taken freely in hot bilious dispositions, they produce flatulencies, thirst, head-achs, and febrile symptoms. In cold sluggish phlegmatic temperaments, they are of service; warming the habit, attenuating viscid humours, and promoting the natural excretions, particularly expectoration and urine. They are likewise powerfully antiseptic, and by virtue of this quality are recommended by some as a salubrious addition to the food in scorbutic cases. Externally, they are employed in cataplasms for suppurating hard tumours: some recommend them also to be rubbed on bald places for promoting the growth of hair. Frederic Hoffman reports, that suppressions of urine, in children, are speedily relieved, by the application of roasted onions to the region of the pubes.
The root, which is the most acrid part of the plant, loses greatly in drying, both of its smell and taste, together with near seven eighths of its weight. It gives out its virtue, by infusion, both to water and to rectified spirit, but not readily, nor completely, to either. In distilla-tion, the whole of its acrimony and peculiar flavour arise with water, and a very considerable part with spirit: the distiled water smells exceeding strongly and offensively of the onion, but no effential oil could be obtained on submit-ting to the operation several pounds of the root. The watery decoction, infpiffated to the consist-ence of an extract, is very mucilaginous, but of scarcely any particular taste; and the taste of the spirituous extract is very weak. The active matter of onions appears therefore to be of a much more volatile kind than that of garlic, with which, in other respects, it nearly agrees.