136 CIRCULATION OF THE BLOOD. 



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 qui- 

 escent ; whence we see the probable reason wherefore nature 

 has instituted the foramen ovale in the foetus, instead of send- 

 ing 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 un- 

 derstand why, when the vessels of the lungs become congested 

 and oppressed, and in those who are affected with serious dis- 

 eases, 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 the lungs, 

 which is, because it is thinner, as having there to undergo 

 filtration. 



Still further ; from the summary which precedes, and by 

 way of satisfying those who are importunate in regard to the 

 causes of the circulation, and incline to regard the power of the 

 heart as competent to everything as that it is not only the 

 seat and source of the pulse which propels the blood, but also, 

 as Aristotle thinks, of the power which attracts and produces 

 it ; moreover, that the spirits are engendered by the heart, and 

 the influxive vital heat, in virtue of the innate heat of the heart, 

 as the immediate instrument of the soul, or common bond and 

 prime organ in the performance of every act of vitality ; in a 

 word, that the motion, perfection, heat, and every property 

 besides of the blood and spirits are derived from the heart, as 

 their fountain or original, (a doctrine as old as Aristotle, who 

 maintained all these qualities to inhere in the blood, as heat 

 inheres in boiling water or pottage,) and that the heart is the 

 primary cause of pulsation and life ; to those persons, did I 

 speak openly, I should say that I do not agree with the common 

 opinion; there are numerous particulars to be noted in the 

 production of the parts of the body which incline me this way, 



