Salicine, when obtained from willow bark, is an expensive agent in the large doses required for horses. The bark of the poplar-tree and the flower-buds of the meadow-sweet also contain it, but not in sufficient proportion to be of any practical value as a source of supply.
Salicylic Acid is obtained by passing a stream of carbonic acid through a heated mixture of caustic soda and carbolic acid, but its natural source of supply is from the oils of winter-green or sweet birch.
In the reduction of high temperatures and the treatment of rheumatism it is the most active remedy known. Some of the obscure lamenesses of a shifting and intermittent character have been quickly banished by its use. Salicine and salicylic acid appear to act in much the same way as quinine, and excessive doses produce the same train of symptoms.
Salicylate of Soda is very much employed in reducing temperatures, but its liability to excite abnormal action of the heart requires special care and observation where its use is to be continued.