4 On the Influence of Air 



thought, which, as agents merely physical, are capable 

 of influencing the human body. To this principle is to 

 be referred every property of animals, which distin- 

 guishes them from inanimate matter. With respect to 

 the brain and nervous system, we all know, that there 

 is nothing resembling them in inanimate matter ; but it 

 will not be found, upon experiment, that the property 

 of muscular fibres, on which the motion of animals de- 

 pends, can be placed in a supposed vital principle, un- 

 less we adopt the idea, that life has its degrees, and that 

 the principle is the same, whether hi the mutilated 

 parts or the entire animal ; and to this principle I must 

 confess myself inclined : for, though sensibility is essen- 

 tial to consciousness, irritability is equally so, and, if 

 the latter does not exist, the former is useless. In our 

 remarks we shall therefore consider man purely as a 

 physical machine, operated upon by external agents, 

 the force of whose action depends upon the excitability 

 of the subject. 



On whatever principle life depends, there could be 

 no lift- without motion : we mean motion of the corpus- 

 cles of bodies, as well as muscular contraction and 







elongation. This motion of the corpuscles of bodies is 

 preserved by the intervention of caloric, which Lavoi- 

 sier and all the modern chemists regard as the universal 

 cause of expansion. Hence the temperature of a body 

 will depend upon the spaces which exist between its 

 corpuscles ; and as the spaces will be in proportion to 

 the greater or less expansibility, so will be the quanti- 

 ties of caloric interposed, over and above what is com- 

 bined to constitute their different properties or capacity. 



