CIRCULATION OF THE BLOOD. 119 



incandescent iron or brass. Whence it would appear that spirits 

 of this nature rather receive their heat from the blood, than that 

 the blood is warmed by these spirits ; such spirits are rather to 

 be regarded as fumes and excrementitious effluvia proceeding 

 from the body in the manner of odours, than in any way as 

 natural artificers 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 ex- 

 perience 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 ne- 

 cessary 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 cali- 

 dum innatum or innate heat, as an instrument of nature avail- 

 able 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 

 anything like commensurate mobility, or which might keep 

 pace with 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 persons see nothing 1 less than the won- 

 derful and almost divine character of the natural operations as 



