SECT. XXIV. THE PROPER JUICE. 463 



blood and peculiar juices. If the blood escapes from 

 the vessels it forms neither flesh nor bones, but 

 tumours ; and if the proper juices escape from the 

 vessels containing them they form neither wood nor 

 bark, but a lump or deposite of inspissated fluid. 



To the sap or to the proper juice, or rather to a 

 mixture of both, we must refer such substances as 

 are obtained from plants under the name of ex- 

 pressed juices, because it is evident that they can 

 corne from no other source. In this state they are 

 generally obtained in the first instance whether 

 with a view to their use in medicine or their applica- 

 tion to the arts. It is the business of the chemist 

 or artist to separate and purify them afterwards ac- 

 cording to the peculiar object he may happen to 

 have in view, and the use to which he purposes to 

 apply them. They contain, like the sap, acetate of 

 potass or of lime, and assume a deeper shade of 

 colour when exposed to the fire or air. The oxy- 

 muriatic acid precipitates from them a coloured and 

 flaky substance as from the sap, and they yield by 

 evaporation a quantity of extract. But they differ 

 from the sap in exhibiting no traces of tannin or 

 gallic acid, and but rarely of the saccharine 

 principle. 



