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 

 further alteration in the living vegetable ; and 

 they 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 con- 

 vertible 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. 



