274 The Older Doctrines [lect. 



the flame of the blood, more by the force of the simile than by 

 reasoning on facts ; nevertheless, as the pupil of Harvey and as 

 a comrade of the chemists of the day, he had laid hold of the 

 view that the heat of the body is the heat of combustion, and 

 in this respect was far above the old idea of the heat innate in 

 the heart to which Descartes clung. He rejects this old idea 

 in the words, " The heart gets its heat from the blood, not the 

 "blood from the heart." 



Having satisfied himself that the active properties of the 

 blood, the vital spirits of the old teaching, are of the nature of 

 flame, the same trust in the force of illustration led him to 

 maintain that the active properties of the nervous system, the 

 animal spirits, were of the nature of light. 



" Although it is clear enough that such spirits are the 

 " causes of animal functions and constitute the basis of the soul 

 " itself, nevertheless it seems very difficult to explain what they 

 " are in their own proper essence, since scarcely anything occurs 

 "in nature with which in all respects they are comparable. 

 " The comparison of these with spirits of wine, of turpentine or 

 " of hartshorn, and the like, is by no means suitable. Besides 

 " that these chemical liquids neither represent the images of 

 " objects, nor exercise any elastic force, as do the animal spirits, 

 " they are moreover less subtle and volatile than these, since 

 " they can be poured or distilled from one vessel into another, 

 "whereas the animal spirits, vanishing directly that life is 

 "extinct, leave no trace of themselves behind. Wherefore we 

 "may far more rightly, according to our hypothesis, say that 

 " these spirits, emitted from the flame of the blood, are like rays 

 " of light, at least these joined with those of wind and air. For 

 "just as light is moulded to the impressions of all visible things, 

 "and air is moulded to the impressions of all audible things, so 

 " the animal spirits receive the images impressed on them, not 

 " only of the above, but also of odours and all tangible qualities, 

 " and deposit them in the common sensorium. But the air or 

 " aerial particles, so long as they are free and unmixed, create 

 " no rush or tumult, yet when closely confined in clouds, or in 

 "machines, or brought into contact with sulphurous and other 

 " elastic corpuscles, being forthwith made wild, burst forth into 



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