Circulation of the Blood 145 



of the tissues ; a conclusion which we are the more 

 disposed to admit, when we see that they so speedily 

 lose any virtue they may possess, and which they had 

 derived from the blood as their source, they are at 

 best of a very frail and evanescent nature. Whence 

 also it becomes probable that the expiration of the 

 lungs is a means by which these vapours being cast 

 off, the blood is fanned and purified ; whilst inspiration 

 is a means by which the blood in its passage between 

 the two ventricles of the heart is tempered by the cold 

 of the ambient atmosphere, lest, getting heated, and 

 blown up with a kind of fermentation, like milk or 

 honey set over the fire, it should so distend the lungs 

 that the animal got suffocated ; somewhat in the same 

 way, perchance, as one labouring under a severe 

 asthma, which Galen himself seems to refer to its 

 proper cause when he says it is owing to an obstruction 

 of the smaller arteries, viz. the vasa venosa et arteriosa. 

 And I have found by experience that patients affected 

 with asthma might be brought out of states of very 

 imminent danger by having cupping-glasses applied, 

 and a plentiful and sudden affusion of cold water [upon 

 the chest]. Thus much and perhaps it is more than 

 was necessary have I said on the subject of spirits in 

 this place, for I felt it proper to define them, and to say 

 something of their nature in a physiological disquisition. 

 I shall only further add, that they who descant on the 

 calidum innatum or innate heat, as an instrument of 

 nature available for every purpose, and who speak of 

 the necessity of heat as the cherisher and retainer in life 

 of the several parts of the body, who at the same time 

 admit that this heat cannot exist unless connected with 

 something, and because they find no substance of any- 

 thing like commensurate mobility, or which might keep 

 pace w r ith the rapid influx and reflux of this heat (in 

 affections of the mind especially), take refuge in spirits 

 as most subtile substances, possessed of the most 

 penetrating qualities, and highest mobility these 



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