Circulation of the Blood 165 



time when the thorax is laid open, and the lungs having 

 collapsed, all the respiratory motions have ceased ; 

 here, nevertheless, for a little while you may perceive 

 the left auricle contracting and emptying itself, and 

 becoming whiter ; but by and by growing weaker and 

 weaker, it begins to intermit, as does the left ventricle 

 also, and then it ceases to beat altogether, and becomes 

 quiescent. Along with this, and in the same measure, 

 does the stream of blood from the divided artery grow 

 less and less, the pulse of the vessel weaker and weaker, 

 until at last, the supply of blood and the impulse of the 

 left ventricle failing, nothing escapes from it. You may 

 perform the same experiment, tying the pulmonary 

 veins, and so taking away the pulse of the left auricle, 

 or relaxing the ligature, and restoring it at pleasure. 

 In this experiment, too, you will observe what happens 

 in moribund animals viz. that the left ventricle first 

 ceases from pulsation and motion, then the left auricle, 

 next the right ventricle, finally the right auricle; so 

 that where the vital force and pulse first begin, there 

 do they also last fail. 



All of these particulars having been recognized by the 

 senses, it is manifest that the blood passes through 

 the lungs, not through the septum [in its course from 

 the right to the left side of the heart], and only through 

 them when they are moved in the act of respiration, 

 not when they are collapsed and quiescent ; whence we 

 see the probable reason wherefore nature has instituted 

 the foramen ovale in the foetus, instead of sending the 

 blood by the way of the pulmonary artery into the left 

 auricle and ventricle, which foramen she closes when 

 the new-born creature begins to breathe freely. We 

 can also now understand why, when the vessels of the 

 lungs become congested and oppressed, and in those 

 who are affected with serious diseases, it should be so 

 dangerous and fatal a symptom when the respiratory 

 organs become implicated. 



We perceive further, why the blood is so florid in 



