substances, which bear the greatest analogy to each other; as between the varieties of sugar, and those of oil; and even between common flax, and the same substance prepared according to the improved process of _Mr. Lee_. This statement is sufficient to show the capability of ultimate analysis, on certain occasions, to identify vegetable bodies; but we are, at present, scarcely advanced far enough in such an investigation, to make it subservient to the detection of vegetable poisons. Nor has our knowledge with regard to proximate analysis, been less successfully advanced. The late researches of the French and German chemists have demonstrated the existence of several new alkaline bodies in the class of vegetable poisons, to which some of these plants appear to be exclusively indebted for their activity, as the _poppy_, _hellebore_, _colchicum_, _&c._; and whose characters are so distinct and striking, as to enable the chemist to recognise their presence by appropriate re-agents. In other cases, the virulence of a plant would appear to depend upon the combination of several[399] proximate principles; while in some few instances there exist in the same individual vegetable, two distinct elements of activity, as illustrated by the interesting history of tobacco. In cases of vegetable poisoning it will occasionally occur, that some remains of the plant may be collected; and seeds, portions of the fungi, and leaves, may be found in the contents of the stomach; whence a knowledge of botany becomes indispensable. This branch of science is, moreover, important to the toxicologist, as enabling him to pursue the study of plants with greater precision; for experience has shewn that there is a wonderful analogy between the structure of those plants which resemble each other in medicinal operation. Thus those which, from their dismal and dusky appearance, have been arranged under the title of _Luridæ_, are in general highly poisonous; they also possess a very peculiar and disagreeable smell, so that Nature has, upon this occasion, kindly given us notice of approaching danger, by means of our senses. Of equal importance with the knowledge of the generic and specific characters, is that of their sensible qualities, and the changes which these latter undergo by pharmaceutical preparation. Cl. III. ACRID, or RUBEFACIENT POISONS. Most of the subjects of this class constitute articles of Materia Medica; so that ignorance on the one hand, and accident on the other, may render them the unexpected source of mischief. With respect to the physiological action of these bodies, the reader has only to refer to our classification at page 207, to perceive that it will not admit of generalization; for each division, it will be observed, contains individuals which belong to the class of acrid poisons.