118 GENERAL FLUID COMPONENTS. [LECT. III. 



juice, which after being exposed to the air for a 

 short time assumes a deep indigo blue tint : and 

 the juice which exudes from incisions in the leaves 

 of the Soccotrine Aloe, yields, by simple exposure, 

 according to the statement of M. Fabroni, a very 

 deep and lively purple dye, so permanent, and re- 

 sisting so completely the action of acids, alkalies, 

 and oxygen gas, that he thinks it may be used as 

 a pigment in miniature painting ; or as a dye for 

 silk, which it will effect without the use of any 

 mordaunt*. 



It is necessary to mention that Mirbel, and 

 some other Botanists, have fallen into an error, in 

 confounding together the proper juice, and the 

 secretions of plants. It is from the proper juice 

 that the secretions are formed ; but it must un- 

 dergo another elaboration, something similar to 

 that which the blood of animals undergoes in their 

 glands, before it is changed into the different se- 

 cretions ; and assimilated into the substance of 

 the plant. Thus, both essential and aromatic oils 

 are found in some parts of the same plant ; muci- 

 lage, resin, tannin, extract, acids and alkalies, and 

 even silica, in other parts ; but these various pro- 

 ductions cannot be considered as the proper juice : 

 they are secretions formed from it. The proper 

 juice of plants is, therefore, " that changed state of 



* Monthly Mg. 1798. 



