252 Mayow 



flow of the animal spirits or from their inordinate 

 motion, as will be more fully stated below. 



For, indeed, nitro-aerial particles seem in a high 

 degree to fit the character of animal spirits, inasmuch 

 as they are very subtle, elastic, and agile. For nitro- 

 aerial particles are suited for entering on very rapid 

 and igneous motion, as we have elsewhere shown. 

 The animal spirits are also of this sort : they pass in a 

 moment through the filaments of the nerves, although 

 these have no visible cavity ; and brought at last to 

 the muscles, cause their instantaneous contraction by 

 their own most rapid motion. 



Further, the animal spirits, like the nitro-aerial 

 particles, are so slender that they are at once dissi- 

 pated and leave no vestige of themselves. I further 

 add that nitro-aerial particles, no less than the animal 

 spirits themselves, are necessary for the sustenance of 

 life. In fact it is difficult to conceive why animals 

 should have such a necessity of breathing air, so that 

 not for a moment can they live without it, unless 

 the nitro-aerial spirits had a primary place in animal 

 life and were the animal spirits themselves. Hence, 

 according as there is need of a greater abundance of 

 animal spirits, as in violent movements, or of less, as 

 when the body is at rest, so nitro-aerial particles must 

 be supplied in greater or in less quantity, and this is 

 the reason why the respiration is so much increased in 

 violent movements. 



Besides, whence, I would ask, is a supply of animal 

 spirits sufficient for continued work obtained unless^ 

 I say, we call to our aid the air, that inexhaustible 

 fountain ? For it is probable that animal spirits are 

 used up in the performance of muscular contraction 

 in much greater quantity than is commonly believed. 

 For I really do not know how a muscle could contract 



