682 PHILOSOPHICAL TRANSACTIONS. [aNNO \6q3. 



are furnished with an air-pump, and can pour off this pale liquid in vacuo, and 

 there stop it up close, you may then preserve it as long as you please, and ex- 

 hibit it to advantage. You may also observe, that as soon as you let in the air, 

 the upper surface becomes first immediately tinged, and so the tincture descends 

 deeper and deeper, until it has penetrated the whole : and this it does the 

 sooner if the glass be wide, and the liquor consequently have a larger surface. 

 Or if you pour it out of one glass into another, the air makes a more sudden 

 change of the whole. 



That liquors should lose their tinctures is not to be wondered at ; for even ink. 

 itself, by standing still, will lose much of its tincture ; and so do the tinctures 

 of many minerals ; that of sulphur, and of salt of tartar, will lose their tinc- 

 tures ; and many vegetables are not long to be preserved, but do grow turbid ; 

 some becoming pale and colourless, leave their menstruums, and precipitate to 

 the bottom, and are not easily if ever recovered. But in our experiment we 

 have some things very uncommon ; a deeply tinged liquor becomes pale and 

 colourless in a few days, without any admission of air, or any other ingredient 

 to disturb it, or to cause any discernible precipitation or separation ; and 

 yet upon the re-admission of the air immediately recovers its former blue 

 tincture. 



The great influence the air has in this experiment induced me to apply it to 

 the great change that is made upon blood ; for it is obvious that there is a great 

 difference in colour between the venal and arterial blood ; the former when first 

 let out of the vein is of a dark colour, and requires some time to be exposed to 

 the air before it obtains a florid red, and that only in the surface contiguous to 

 the air. The observation is certain and unerring, that the venal blood, as it 

 passes the right ventricle, at its entrance into the lungs, is of a very opaque and 

 blackish colour, and in its passage through th» lungs, before it reaches the left 

 auricle, it is changed into a very florid and bright red ; and it has been often 

 observed, that persons that have vomited blood, on a rupture of some capillary 

 vessels of the lungs, have discharged a very frothy blood, and at the same time 

 of a bright scarlet red : its being frothy argues an admixture of air; and its 

 being red was owing to the tinging quality of the air. To expect that this 

 change should be made in the heart by any local ferment, or vital flame, is 

 fruitless : because the change is performed before its arrival there, and because 

 the structure of the heart denotes that it is principally designed for projecting 

 the blood, in order to a circulation through those various arteries which are 

 branched from the heart. If we consider the structure of the lungs, we shall 

 soon discover them to be a pneumatic engine, principally designed for taking 

 in air, and that in great quantities. It is true, we may call the lungs a contex- 



