182 Dr. R. D. Thomson on Parietin, a Yellow Colouring Matter. 



upon whom the contingency does fall, gets all that those whom for- 

 tune has exempted from it have lost in hard money, and is thus 

 enabled to sustain an event which would otherwise overwhelm him.*' 

 This well defines the principle of all insurance. I may be somewhat 

 of an enthusiastic admirer of the system, but if one will only consider 

 what the state of society would be without any such protection as it 

 affords, he will, I think, feel how much we are indebted to the truth- 

 investigating labours of the statist, for so great an ally of prudence, 

 so useful a guardian of industry. 



13th December, 1843, — The President in the Chair. 



The following were elected Members of the Society: — Messrs. Jas. 

 Church, David Thomson, B.A., Charles Griffin, "Walter Nielsen, Wm. 

 Dunn, James Bogle, and Charles Maxwell Graham. 



According to previous arrangement, Mr. Crum moved that a Botani- 

 cal Section should be added to the Society, and Mr. Gourlie was 

 requested to convene the Members who intended to join it, for the 

 purpose of choosing their office-bearers, and making other necessary 

 arrangements. 



Mr. James Thomson, C.E., described two iron lattice bridges, illus- 

 trated with models, which have been erected, one in Scotland, the 

 other in Ireland. Mr. Stenhouse exhibited a Davy lamp, constructed 

 with mica plates, which appeared well adapted for the purposes of the 

 miner. 



The following paper was then read : — 



XLIII. — On Parietin, a Yellow Colouring Matter, and on the Inorganic 

 Food of Lichens. By Robert D. Thomson, M.D. 



The objects of the present paper are, 1st, to endeavour to prove that, 

 contrary to the usually received opinion, the class of plants termed 

 lichens require inorganic matter as part of their food, which they 

 must derive from the localities upon which they are fixed ; and 2d, to 

 describe the yellow colouring matter obtained from the yellow wall 

 lichen, and to detail its properties, composition, and application as a 

 test for alkalies. 



Although chemists are acquainted with several yellow colouring 

 matters, few of them have been separated in a pure state, and analysed. 

 This arises from the difficulty of procuring such substances in the 

 same state as that in which they existed in the plant from which they 

 are extracted — depending principally on the facility with which they 

 unite with oxygen, and on their consequent conversion into a body of 

 inferior beauty, and of an uncrystallized structure. The yellow colour- 

 ing matters which have hitherto been analysed, are derived from 



