226 The Rise of the Modern [lect. 



blood vessels, and he discusses at length how the rhythmic 

 movement, the alternate expansion and contraction of the chest 

 affects the condition of blood vessels in the lungs, and so the flow 

 through them. And he takes credit to himself for being the first 

 to shew that so far from breathing having a cooling effect on the 

 blood, the friction engendered by the passage of blood through 

 the lungs is one of the chief sources of the heat of the body. 



Thus the great chemist of the day was, by the influence of 

 a theory, led away from the true solution of one of the most 

 conspicuous chemical problems of physiology. And this was 

 the case, although he had put his foot on the right path. 

 Discussing the uses of air, he dwells briefly on the question 

 whether something may not in inspiration be given up to the 

 blood, just as in expiration there is, as he admits, a "transpiration 

 of aquosity in the form of vapour" ; but he concludes that any 

 such entrance is of little moment ; and he sums up as follows. 



" As however it is quite evident that air thus takes part in 

 " and contributes to this whole business of breathing in no 

 "other than a formal manner, as the phrase is" (that is in a 

 mechanical manner), " so, as to whether, where and how it may 

 " seem to add something in the way of mere matter, we have 

 "already made a remark or two. Meanwhile it is wholly clear, 

 " from every point of view, that that something is neither 

 "great in quantity nor dense in quality, nor indeed anything 

 "different from the true nature of atmospheric air, which it 

 " must necessarily be if breathing supplied any kind of spirit to 

 " the blood. If it be anything it must be something much more 

 * simple, namely a certain principle called phlogiston. Never- 

 " theless in respect even to this, doubts against it of no less 

 " weight than arguments in favour of it present themselves. 

 " For this principle does not abound in the air in sufficient 

 " quantity to be able at each breath to supply and add to the 

 " blood an amount of itself of any moment. This is a posteriori 

 " clear from the fact that only a very little of this matter of 

 " phlogiston can be received into even a large quantity of air, 

 "even in a place where it is sufficiently collected in it, as 

 " when inflammable things are burnt. However these things 

 "may be, these considerations, interesting perhaps to the 



