This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
A number of plants exude on incision liquids that have been contained in certain specialised cells. These liquids differ in their composition from the latex contained in laticiferous tissue and also from the oil, oleo-resin, or oleo-resinous emulsions secreted in cells, glands, or ducts. Some of them contain substances of medicinal value, as, for instance, various species of Aloe, Eucalyptus, etc.; these yield when dried drugs that, for want of a better term, have been designated ' dried juices.' In many cases tannin forms the chief constituent as it does in the various kinos; in others, particular substances not produced in other natural orders or even genera are found, such as aloin.