On Sal Nitriim and Nitro- Aerial Spirit 95 



they move towards the south till at last they reach the 

 lower earth for the various needs of animals. And 

 this seems to be the reason that the north wind is very 

 dry and cold, since it brings with it air which is heavy 

 with nitro-aerial particles and these extremely cold and 

 dry. And as aerial particles are thus raised aloft when 

 deprived of nitro-aerial spirit and being then anew 

 impregnated with it return thence to the lower regions^ 

 the aerial particles seem to circulate like a macrocosmic 

 blood in a perpetual circuit, and even the air itself, as 

 in its circulation it takes in nitro-aerial spirit, in some 

 sense breathes. 



CHAPTER VIII 



OF NITRO-AERIAL SPIRIT IN SO FAR AS IT IS 

 BREA THED BY A NIMA LS 



Hitherto we have treated of nitro-aerial spirit and 

 its effects upon plants and other natural things — it 

 remains for us to inquire into the office it fulfils in 

 the case of animals. In our treatise on Respiration 

 published some time ago various considerations in- 

 duced me to maintain that the chief use of respiration, 

 that, namely, which makes it so necessary, is that 

 particles of a certain kind, absolutely necessary for the 

 support of animal life, may be separated from the air 

 by means of the lungs and mixed most minutely with 

 the mass of the blood ; and in confirmation of our 

 opinion we brought forward in the previous chapter 

 experiments by which it was shown that the air 

 expelled from the lungs of animals is deprived of 



