ON GENERATION. 375 



pulsion of the blood, as clearly appears in all animals furnished 

 with red blood ; and the office of the pulsating vesicle in the 

 generation of the chick ab ovo, as well as in the embryos of 

 mammiferous animals, is not different, a fact which I have re- 

 peatedly demonstrated to others, showing the vesicula pulsans 

 as a feeble glancing spark, contracting in its action, now forc- 

 ing out the blood which was contained in it, and again relaxing 

 and receiving a fresh supply. 



The supremacy of the blood farther appears from this, that 

 the pulse is derived from it ; for, as there are two parts in a 

 pulsation, viz. : distension or relaxation, and contraction, or 

 diastole and systole, and, as distension is the prior of these two 

 motions, it is manifest that this motion proceeds from the blood; 

 the contraction, again, from the vesicula pulsans of the embryo 

 in ovo, from the heart in the pullet, in virtue of its own fibres, 

 as an instrument destined for this particular end. Certain it 

 is, that the vesicle in question, as also the auricle of the heart 

 at a later period, whence the pulsation begins, is excited to the 

 motion of contraction by the distending blood. The diastole, 

 I say, takes place from the blood swelling, as it were, in con- 

 sequence of containing an inherent spirit, so that the opinion 

 of Aristotle in regard to the pulsation of the heart, namely, 

 that it takes place by a kind of ebullition, is not without some 

 mixture of truth ; for what we witness every day in milk heated 

 over the fire, and in beer that is brisk with fermentation, 

 comes into play in the pulse of the heart ; in which the blood, 

 swelling with a sort of fermentation, is alternately distended 

 and repressed ; the same thing that takes place in the liquids 

 mentioned through an external agent, namely adventitious 

 heat, is effected in the blood by an intimate heat, or an innate 

 spirit ; and this, too, is regulated in conformity with nature 

 by the vital principle (anima), and is continued to the benefit 

 of animated beings. 



The pulse, then, is produced by a double agent : first, the 

 blood undergoes distension or dilatation, and secondly, the 

 vesicular membrane of the embryo in the egg, the auricles and 

 ventricles in the extruded chick, effect the constriction. By these 

 alternating motions associated, is the blood impelled through 

 the whole body, and the life of animals is thereby continued. 



Nor is the blood to be styled the priniigenial and principal 



