INTRODUCTION. 49 



them; enough has been said to explain the plan to be carried out, and more 

 fully elucidated, in the progress of the work. 



Pharmaceutic Botany. 



The relations existing between the medical properties of vegetables and 

 their structure, have long attracted the notice of the learned, and it was early 

 declared, that plants closely resembling each other in their external appear- 

 ance, were possessed of analogous qualities. The first to promulgate this 

 doctrine was Camerarius, according to Decandolle, and Cassalpinus, accord- 

 ing to Dierbach. Linnaeus expressly says on this subject : " Plants that 

 agree in genus, agree in quality ; those of the same natural order have nearly 

 similar properties ; and those of the same natural class are somewhat similar 

 in their powers." Decandolle and Lindley hold much the same sentiments, 

 in which they are supported by numerous other and esteemed writers. That 

 these opinions are correct to a great extent, must be admitted ; but on the 

 other hand, the exceptions are both numerous and important, for whilst in 

 some orders there is found the most striking consonance between the external 

 form and the remedial qualities of the species composing it, in others, it has 

 been shown, that the most dissimilar properties occyr. Thus, in the Solance, 

 the fruit of Capsicum is pungent and stimulant, and that of Atropa, narcotic 

 and poisonous. This dissimilarity extends even to genera, though less fre- 

 quently. So, also, plants differing widely in their external appearance and 

 structure, furnish products of analogous medical qualities. Thus, turpentines 

 are furnished by trees of very distinct orders, and even classes, and manna 

 is equally a secretion of a Frazinus and a Eucalyptus. 



It cannot be admitted, as is asserted by Lindley, that " a knowledge of one 

 plant is a guide to the practitioner, which enables him to substitute with con- 

 fidence, some other plant that is naturally allied to it." All, that in the pre- 

 sent state of our knowledge can be conceded, is, that as a general rule, plants 

 of the same order agree in their remedial qualities, though this is not univer- 

 sally the case. 



Many attempts have been made to classify medicinal plants and their pro- 

 ducts, by their sensible properties; namely, their colour, taste, andT>dour, 

 but none of these have been successful, as it has been found that in all cases, 

 the exceptions are so numerous as to render such arrangements of little prac- 

 tical benefit. This has arisen not only from the difficulty of describing and 

 defining sensations, but also from the fact that two or more articles having the 

 same sensible property, may differ widely from each other in action on the 

 system. Thus, for instance, morphia, quinia, and aloes, are all bitter, and 

 yet the first is a powerful narcotic, the second an efficacious tonic, and the 

 third an active purgative. The best examples of this method of arranging 

 plants, are found in a paper by/.pr. Osborne, {Trans. Assoc, fyc. King <J- 

 Queen's College, V.) and an Essay on the subject by Dr. Graves, (Supp. 

 Edin. Dispen.) 



Collection and Preservation of Plants. 



Vegetables used as medicinal agents, should, as far as possible, be collected 

 every year, and those previously obtained, rejected, as many vegetable sub- 

 stances are altered and deteriorated by keeping. A variety of circumstances 

 exercise an influence on the activity, of a plant, as the locality in which it 



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