RETURN OF THE SAP. 43 



latter structures may be compared to the bones 

 of animals, composing by their union the solid 

 frame work, or skeleton of the organized system. 

 The woody fibres do not seem to be capable of 

 farther alteration in the living vegetable, and 

 are never, under any circumstances, taken up 

 and removed to other parts of the system, as is 

 the case with nutritive matter of a more conver- 

 tible kind. 



The sap holds in solution, besides carbona- 

 ceous matter, some saline compounds and a few 

 earthy and metallic bases : bodies which, in how- 

 ever minute a quantity they may be present, 

 have unquestionably a powerful influence in 

 determining certain chemical changes among 

 the elements of organic products, and in im- 

 parting to them peculiar properties ; for it is now 

 a well ascertained fact that a scarcely sensible 

 portion of any one ingredient is capable of pro- 

 ducing important differences in the properties of 

 the whole compound. An example occurs in 

 the case of gold, the ductility of which is totally 

 destroyed by the presence of a quantity of either 

 antimony or lead, so minute as barely to amount 

 to the two thousandth part of the mass ; and even 

 the fumes of antimony, when in the neighbour- 

 hood of melted gold, have the power of destroy- 

 ing its ductility.* In the experiments made by 



* Hatchett. 



