240 LECTURE V. 



1755-6, when making drawings of the 

 changes which took place in the incubated 

 eggy he was particularly struck with the well 

 known fact, that the yolk and white, which 

 we cannot suppose to be organized, did not 

 putrify ; and this led him to believe that 

 fluid and semi-fluid substances might have 

 a principle of life diffiised through them. 



Every one must be convinced that the 

 power of the heart is very considerable, 

 even from observing the thickness and 

 compactness of its fleshy structure. Dr. 

 Hales estimated its force as equal to a little 

 more than 70lbs. That it could not act 

 with the enormous force which some have 

 attributed to it, Mr. Hunter inferred from 

 finding that a force of 90lbs. burst the in- 

 elastic part of the aorta. Mr. Hunter be- 

 lieved that the forcible projection of an 

 additional quantity of blood from the heart 

 into the arteries, produced a sudden mo- 

 tion in the whole column contained in these 

 tubes, and occasioned their almost simul- 

 taneous pulsation in every part. He could 

 not doubt that if they were contracted, they 



