138 WILLIAM HARVEY 



fluid, by reason of the variety of organic parts, or of the 

 density of the substance; but the pulsations occur unfre- 

 quently, and sometimes in consequence of the cold not at 

 all, an arrangement the best adapted to them as being of 

 a doubtful nature, so that sometimes they appear to live, 

 sometimes to die; sometimes they show the vitality of an 

 animal, sometimes of a vegetable. This seems also to be 

 the case with the insects which conceal themselves in winter, 

 and lie, as it were, defunct, or merely manifesting a kind 

 of vegetative existence. But whether the same thing hap- 

 pens in the case of certain animals that have red blood, 

 such as frogs, tortoises, serpents, swallows, may be very 

 properly doubted. 



In all the larger and warmer animals which have red 

 blood, there was need of an impeller of the nutritive fluid, 

 and that, perchance, possessing a considerable amount of 

 power. In fishes, serpents, lizards, tortoises, frogs, and 

 others of the same kind there is a heart present, furnished 

 with both an auricle and a ventricle, whence it is perfectly 

 true, as Aristotle has observed/ that no sanguineous animal 

 is without a heart, by the impelling power of which the 

 nutritive fluid is forced, both with greater vigour and 

 rapidity, to a greater distance; and not merely agitated by 

 an auricle, as it is in lower forms. And then in regard 

 to animals that are yet larger, warmer, and more perfect, 

 as they abound in blood, which is always hotter and more 

 spirituous, and which possess bodies of greater size and 

 consistency, these require a larger, stronger, and more 

 fleshy heart, in order that the nutritive fluid may be pro- 

 pelled with yet greater force and celerity. And further, 

 inasmuch as the more perfect animals require a still more 

 perfect nutrition, and a larger supply of native heat, in 

 order that the aliment may be thoroughly concocted and 

 acquire the last degree of perfection, they requirtr-d both 

 lungs and a second ventricle, which should force the nu- 

 tritive fluid through them. 



Every animal that has lungs has, therefore, two ven- 

 tricles to its heart one right, the other left; and wherever 

 there is a right, there also is there a left ventricle; but 



1 De Part. Animal., lib. Hi. 



