Motion of the Heart and Blood 97 



further, as in snails, whelks, shrimps, and shell-fish, 

 there is a part which pulsates a kind of vesicle or 

 auricle without a heart slowly indeed, and not to be 

 perceived save in the warmer season of the year. In 

 these creatures this part is so contrived that it shall 

 pulsate, as there is here a necessity for some impulse to 

 distribute the nutritive fluid, by reason of the variety of 

 organic parts, or of the density of the substance ; but 

 the pulsations occur unfrequently, 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 manifest- 

 ing a kind of vegetative existence. But whether the 

 same thing happens in the case of certain animals 

 that have red blood, such as frogs, tortoises, serpents, 

 swallows, may be made a question without any kind of 

 impropriety. 



In all the larger and warmer, because [red-] blooded 

 animals, 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, 1 

 that no [red-] blooded 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; it is 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 ever hotter and more 

 spirituous, and possess bodies of greater size and con- 

 sistency, they require a larger, stronger, and more 



1 De Part. Animal, lib, iii. 



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