Page:The Works of William Harvey (part 1 of 2).djvu/480

 tardation, in turbulence and strength, or debility, it is manifest that the blood perceives things that tend to injure by irritating, or to benefit by cherishing it. We therefore conclude that the blood lives of itself, and supplies its own nourishment ; and that it depends in nowise upon any other part of the body, which is either prior to itself or of greater excellence and worth. On the contrary, the whole body, as posthumous to it, as added and appended as it were to it, depends on the blood, though this is not the place to prove the fact ; I shall only say, with Aristotle, l that ' ' The nature of the blood is the undoubted cause wherefore many things happen among animals, both as regards their tempers and their capacities " To the blood, therefore, we may refer as the cause not only of life in general, inasmuch as there is no other inherent or influxive heat that may be the immediate instrument of the living principle except the blood, but also of longer or shorter life, of sleep and watching, of genius or aptitude, strength, &c. " For through its tenuity and purity," says Aristotle in the same place, " ani- mals are made wiser and have more noble senses ; and in like manner they are more timid and courageous, or passionate and furious, as their blood is more dilute, or replete with dense fibres."

Nor is the blood the author of life only, but, according to its diversities, the cause of health and disease likewise : so that poisons, which come from without, such as poisoned wounds, unless they infect the blood, occasion no mischief. Life and death, therefore, flow for us from the same spring. " If the blood becomes too diffluent," says Aristotle, 2 "we fall sick; for it sometimes resolves itself into such a sanguinolent serum, that the body is covered with a bloody sweat ; and if there be too great a loss of blood, life is gone." And, indeed, not only do the parts of the body at all times become torpid when blood is lost, but if the loss be excessive, the animal necessarily dies. I do not think it requisite to quote any particular experiment in confirmation of these views : the whole subject would require to be treated specially.

The admirable circulation of the blood originally discovered by me, I have lived to see admitted by almost all ; nor has

1 De Part. Anim. lib. ii, cap. 4. a Hist. Anim. lib. iii, cap. 19.