Oil Muscular Motion and Animal Spirits 245 



through the lungs although they do not move. Nor 

 is it, as some one might say, that respiration is 

 increased in violent exercise to cool the heated blood, 

 for it would follow from that that in febrile heat, 

 when the blood is as it were on fire, there would also 

 be need of more intense respiration. And, moreover, 

 we have shown above that inspired air tends rather to 

 the heating than to the cooling of the blood, so that 

 it should rather be said that by the contraction of the 

 muscles, often repeated in violent movements, the 

 blood is deprived of fermentative particles and in 

 some measure coagulated ; and that there is need of 

 more intense respiration for this reason, namely, that 

 the loss of the fermentative particles being again 

 repaired, suitable fermentation may be excited in the 

 blood. Hence, indeed, it follows that the nitro-aerial 

 particles, upon which the fermentation of the blood 

 depends, are separated from the mass of the blood in 

 violent movements, are spent in the contraction of 

 the muscles, and are lost. 



From what has been said, we conclude that nitro- 

 aerial particles are necessary for the performance of 

 muscular contraction, and this will be still more 

 manifest from what follows. 



I think it must be conceded that the motion 

 of the muscles is brought about by particles of 

 different kinds mixed with one another, for indeed I 

 cannot imagine how else animal motion could be 

 produced. For as to elasticity and weight, by which 

 automata are set in motion, neither of them can have 

 a place in the animal structure, inasmuch as motion 

 produced by them would soon come to an end. 

 Therefore it seems that we must conclude that the 

 motive function is effected by particles of different 

 kinds, mixed together, on the determination of the 



