On Muscular Motion and Animal Spirits 249 



buted to the motion of the body itself, but indeed in 

 animal motion there is no such friction of the parts 

 (from which alone heat arises) as could account for so 

 intense a fervour. We must, therefore, believe that 

 the heat of strongly contracting muscles comes from 

 nitro-aerial particles, at that time much agitated in 

 the muscles ; as I have endeavoured elsewhere to 

 show that every kind of heat arises from their 

 motion. 



I may here note by the way that the ancients, not 

 altogether without reason, supposed that the source 

 of vital heat was in the heart ; not that a sort 

 of Biolychnium, whatever that may be, constantly 

 flamed in its sacred cloisters, but that, inasmuch as 

 the heart is unweariedly at work in continuous labour 

 for keeping up the motion of the blood, the nitro- 

 aerial and the sulphureous particles effervesce con- 

 tinuously in its muscular part, and that by their 

 motion a notable heat must be produced. 



Further, from the foresaid hypothesis a reason 

 can be deduced why the sweat given out in violent 

 movements is of a saline character, and very penetrat- 

 ing. For the extremely subtle nitro-aerial, as also 

 the saline-sulphureous particles, by which when mixed 

 together the contraction of the muscles is produced, 

 when forced out along with the serous liquid, render 

 it acrid and very penetrating. The reason why the 

 sweat is acido-saline seems to be that the volatile salts 

 of the blood, intimately combined with sulphureous 

 particles, are partly brought to a liquid state by the 

 effervescence which takes place in the muscular 

 contraction, in the way elsewhere described. 



From what has hitherto been said, it is to some 

 extent proved that muscular motion depends on 

 nitro-aerial and saline-sulphureous particles mutually 



