OBSERVATIONS ON PHYSIOLOGY. 



ON LIFE AND THE LIVING PRINCIPLE. 



Analogy of Life to Combustion. 



In the works of Nature, where we see a similarity in principle, or effects 

 produced from similar causes, it is reasonable to suppose that they 

 [those works] are similar in their great principles, and therefore may 

 arise from one cause. If this is reasonable, we see that what we have 

 been saying with regard to fire and air in the Introductory Treatise, 

 may be applied to the lungs. There we explained in what manner air 

 has an effect upon fire ; but, without being able to explain this, we see 

 that air, some way or other, is of great service to fire. It is from this 

 that we draw the analogy : and what we want to do here is to see if 

 the explanation of the one will apply to the other. 



I would consider Life as a Fire, or something similar, which might 

 for distinction's sake be called Animal Fire. 



Like common fire, it wants a constant supply, without which it would 

 be extinguished ; and, like common fire, it seems to be let loose in the 

 lungs, so as to be fitted for animal life, before it sets out on its great 

 office : and this letting loose of the animal fire seems to depend upon the 

 air, as much and in the same manner as common fire. So that, instead 

 of something vivifying being taken fromthe air, the air carries off that 

 principle which encloses and retains this animal fire. I do not mean 

 real and actual fire ; but something that is similar, and is effected and 

 brought about much in the same manner. And by understanding the 

 one, we are led, in some measure, to the knowledge of the other ; so 

 that the aliment we take in has in it, in a fixed state, the real life ; and 

 this does not become active until it has got into the lungs ; for there it 

 is freed from its prison 1 . 



1 [Both Hippocrates (Opera, torn. i. p. 112) and Harvey (Exercit. 71) were in- 

 fluenced by this analogy of the animal operations to the consumption of bodies by 

 fire, and identified the vital principle with that element, as the Calidum inna- 

 turn, See.'] 



I 



