21 



It was obvious, therefore, that a btrong saline solution could change 

 the colour of the blood from venous to arterial without the contact of 

 oxygen, or indeed of any gas whatever. 



But in blood, the colouring matter is in contact, not with a strong 

 saline solution, but with a very dilute one, viz. the serum. It was 

 necessary, therefore, to see whether the washed clot, placed in con- 

 tact with serum or a weak solution of salt, in the same gases, would 

 change its colour. On repeating the experiments, both with serum 

 and a solution of salt in water of equal strength to the serum, no 

 change whatever took place, until atmospheric air or oxygen gas was 

 aduiiited. 



The conclusions of Dr Stevens, therefore, must be somewhat mo- 

 dified. It is true, as he states, that the presence of saline matter is 

 essential to the change of colour : But it is obvious, that there is an 

 essential difference between that change as it occurs in the lungs, 

 where serum is present, and as it appears out of the body when a 

 strong saline solution is employed. In the former case, oxygen is 

 necessary : In the latter, the change of colour is independent of the 

 presence of any gas whatever. We must, therefore, be cautious how 

 we reason by analogy from the one class of phenomena to the other. 



April 15. 



PiiOFESSOR RUSSELL, Vice-President, in the Chair. 

 The following Donations were presented : — 



Memoires presentes par divers Savans k I'Academie Royale des Sci- 

 ences de rinstitut de France. Tome 3. — From the Royal Insti- 

 tute of France. 



Quarterly Journal of Agriculture, 3 vols., and Prize Essays and 

 Transactions of the Highland Society of Scotland (New Series), 

 3 vols. — From the Society. 



The following Communications were then read : — 

 1. Observations on the Lines of the Solar Spectrum, and 

 on those produced by the Earth's Atmosphere, and by 

 the Action of Nitrous Acid Gas. By Sir David Brewster, 

 LL.D.F.R.S. 



The author was led, in prosecution of his researches on the absorp- 

 tive action of transparent media of light, which have been partly 

 communicated in previous papers to the Society, to examine the 



