244 Mayow 



CHAPTER IV 



THE ANIMAL SPIRITS BY WHICH MUSCULAR CON- 

 TRACTION IS PRODUCED CONSIST OF NITRO- 

 A ERIA L PAR TICLES. I NCI DENT A LLY, AS TO THE 

 MOTION OF THE BRAIN 



As to the nature of the Animal Spirits, we may 

 conclude that they, so far at least as they contribute 

 to animal motion, consist of Nitro-aerial Spirit. But 

 that this may be more clearly understood, let us first 

 suppose that nitro-aerial particles, which we have 

 elsewhere shown to be passed into the blood by 

 respiration, have also some share in setting up the 

 performance of motionj as has long been our opinion. 

 For, indeed, we have remarked a good while ago, in 

 our Treatise on Respiration, that animals in the more 

 violent exercises, as when much urged in running, 

 find of all things a necessity of very much increased 

 respiration ; and the cause of this seems to be, that in 

 violent movements the nitro-aerial particles are separ- 

 ated from the mass of the blood to set up the contraction 

 of the muscles and are used up, so that there is need of 

 more frequent respiration by which the blood may 

 repair its losses, and have restored to it anew nitro-aerial 

 particles for carrying on the function of motion. For 

 the purpose of the increased respiration in violent exer- 

 cises is not that the blood coming in greater abundance 

 to the central organs and pushed on by the more fre- 

 quent collapse of the lungs, should pass through them 

 more easily ; for in febrile heat, when, namely, the 

 blood circulates in a most furious whirl, the respiration 

 is nevertheless no more intense than usual : indeed, 

 it has been elsewhere shown that the blood can pass 



