238 Dr. Thomson on the Vinegar Plant. 



Here we have an opposite result from the changes produced by water, the 

 kernel being the most impure. The nature of the surrounding matter to 

 such nodules would require to be also considered, when we might see the 

 course of a similar polarization between it and the centre, inducing the 

 formation of that pure line of crystalline pyrites crust, which separates 

 the centre from the external rock or mineral, in the same manner as in 

 the former specimen. 



We have thus, in a somewhat desultory manner, recorded the results 

 of observations made during some investigations for another purpose. 

 The changes which are taking place in these loose stones are, we believe, 

 taking place in the rocks forming the crust of the earth, and if these 

 changes be found analogous, observations may be more easily extended, 

 being more within every individual's reach. 



We must not be supposed in the meantime as either objecting to or 

 supporting any particular theory of the filling of mineral veins. If they 

 have been fiUed by the minerals, whether metallic or otherwise, being 

 dissolved out of the rock, and carried in solution to the fissures, where 

 they become reduced, either by ordinary crystallization or electrical 

 influence, they must have been diffused through the rocks originally. 

 The solvent that would dissolve out all the metals that are found in 

 veins from such rocks in which the vein exists, without dissolving in the 

 first instance many of the principal earthy minerals, even although ac- 

 companied with strong magnetic currents, it would be difficult to suggest. 



There are, again, so many strong and practical objections to the igneous 

 and sublimation theories, in almost every step we take, that we think it 

 best to pause until a more rigid chemical investigation has been made 

 of substances under every condition in which they may be found, as 

 the practice of theorizing upon external observation is as likely to lead 

 to error as to truth. 



March 17, 1852.— i/?-. Crum in the Chair. 

 The foUowing communication was made : — 



XXIX. — Notice ofilie Vinegar Plant. By Dr. R. D. Thomson. 

 The Vinegar Plant, or mother of vinegar, belongs, according to 

 Kiitzing, to the genus Ulviiia, characterized by consisting of a compact 

 lubricous layer of very minute granules. Ulvina aceti, at first mem- 

 branaceous, then forming a compact stratum, vertically divided into 

 dichotomous branches densely aggregated. He describes it as occurring 

 always in the vinegar fermentation, upon the surface of the vinegar pot. 

 The formation of the vinegar plant commences with that of the vinegar. 

 It begins as a thin pellicle on the surface of the fluid, with little consis- 

 tence. Under the microscope it consists of small globules, which are six 



