246 THE FLUID COMPONENTS OF PLANTS. 



The proper juice of plants is, that changed state of 

 the sap, after it has been exposed to the air and light, 

 in the leaf and is returning from it to form the differ- 

 ent secretions. The organs by which the secretion is 

 performed are probably glands ; and the secreted 

 fluids themselves are deposited in cells in different 

 parts of the plant, particularly in the bark, and the 

 roots ; these parts acquiring different medical virtues, 

 from the matters thus lodged in them. 



It is almost as impossible to obtain the proper juice 

 of plants free from sap, as it is to procure the sap free 

 from the proper juice ; this, however, in the season 

 in which it can be obtained in most abundance, is not 

 so liable to be diluted or mixed with sap as at other 

 times ; and therefore it is in the warmest times in 

 summer, that it ought to be taken for the purpose of 

 examining its properties. In an accurate examina- 

 tion of the proper juice of plants, M. Chaptal found 

 that in no two kinds of plants does it agree as far as 

 its sensible qualities are considered ; but as it is in the 

 leaf that the change from sap into the proper juice oc- 

 curs, so its sensible qualities are modified according to 

 the action which takes place in that organ ; and that this 

 should differ is not surprising if we consider the great 

 difference of the structure of leaves. In one particu- 

 lar, however, Chaptal found that all the specimens he 

 examined agreed. When he poured into them oxy- 

 genated muriatic acid, a very considerable white pre- 

 cipitate fell down ; which had the appearance of fine 

 starch, when washed and dried, and did not change 

 when kept for a length of time. It was insoluble in 

 water, and not affected by alkalies. Two thirds of it 

 were dissolved in heated alkohol ; and these were 

 evidently resinous, as they were again precipitated 

 from the spirituous solvent by water. The third part, 

 which continued insoluble in both alkohol and water, 



