x PREFACE, 
fully to comprehend, it is rather owing to the im- 
perfection of science, than to the irregularity of 
nature. 
A. few illustrations of this point, taken from 
general facts already ascertained, will place the 
subject in a clearer light. 
The chemical substances, known by the names 
of Gum Mucus and Fecula, are constantly emol- 
lient, demulcent, and nutritious. They manifest 
these qualities even when extracted from acrid 
and poisonous vegetables, as in Arum, Calla, and 
Jatropha. : 
Sugar is nutritious and demulcent, — When 
subjected to a spontaneous chemical change by 
the vinous fermentation, it is universally a strong 
diffusible stimulus. < : on 
_ Fixed oils are emollient and laxative. Also 
nutritious, - es 
_ Folatile oils on the contrary are acrid, stimu- 
lating, heating, and antispasmodie. ibigliesdh co eit 
: Tannin and the Gallic acid are uniformly an- 
tiseptic and powerfully astringent. 
The Acetous, Citric, Tartaric and similar veg- 
etable acids are refrigerant and antiseptic, ) 
| Bitter Extractive substances are usually tonic. 
Resins, which are bitter and acrid, are com- 
monly cathartic. 
