Employment is Nature’s physician, and is essential to human happiness.

Every animal is sad after coitus except the human female and the rooster.

That physician will hardly be thought very careful of the health of others who neglects his own.

That which is grows, while that which is not becomes.

The best physician is also a philosopher.

The physician is Nature’s assistant.

The plexus called rectiform [rete mirabile] by anatomists, is the most wonderful of the bodies located in this region. It encircles the gland [the hypophysis] itself and extends far to the rear; for nearly the whole base of the encephalon has this plexus lying beneath it. It is not a simple network but [looks] as if you had taken several fisherman’s nets and superimposed them. It is characteristic of this net of Nature’s, however, that the meshes of one layer are always attached to those of another, and it is impossible to remove anyone of them alone; for, one after another, the rest follow the one you are removing, because they are all attached to one another successively.

Work is nature’s physician; it is essential to human health and happiness.

Employment, which Galen calls 'Nature's Physician,' is so essential to human happiness that indolence is justly considered as the mother of misery.

Casting off the dark fog of verbal philosophy and vulgar medicine, which inculcate names alone ... I tried a series of experiments to explain more clearly many phenomena, particularly those of physiology. In order that I might subject as far as possible the reasonings of the Galenists and Peripatetics to sensory criteria, I began, after trying experiments, to write dialogues in which a Galenist adduced the better-known and stronger reasons and arguments; these a mechanist surgeon refuted by citing to the contrary the experiments I had tried, and a third, neutral interlocutor weighed the reasons advanced by both and provided an opportunity for further progress.

And I do not take my medicines from the apothecaries; their shops are but foul sculleries, from which comes nothing but foul broths. As for you, you defend your kingdom with belly-crawling and flattery. How long do you think this will last? ... let me tell you this: every little hair on my neck knows more than you and all your scribes, and my shoebuckles are more learned than your Galen and Avicenna, and my beard has more experience than all your high colleges.

He that knows the secrets of nature with Albertus Magnus, or the motions of the heavens with Galileo, or the cosmography of the moon with Hevelius, or the body of man with Galen, or the nature of diseases with Hippocrates, or the harmonies in melody with Orpheus, or of poesy with Homer, or of grammar with Lilly, or of whatever else with the greatest artist; he is nothing if he knows them merely for talk or idle speculation, or transient and external use. But he that knows them for value, and knows them his own, shall profit infinitely.

At this point, however, I have no intention whatever of criticizing the false teachings of Galen, who is easily first among the professors of dissection, for I certainly do not wish to start off by gaining a reputation for impiety toward him, the author of all good things, or by seeming insubordinate to his authority. For I am well aware how upset the practitioners (unlike the followers of Aristotle) invariably become nowadays, when they discover in the course of a single dissection that Galen has departed on two hundred or more occasions from the true description of the harmony, function, and action of the human parts, and how grimly they examine the dissected portions as they strive with all the zeal at their command to defend him. Yet even they, drawn by their love of truth, are gradually calming down and placing more faith in their own not ineffective eyes and reason than in Galen’s writings.

For, however much we may clench our teeth in anger, we cannot but confess, in opposition to Galen’s teaching but in conformity with the might of Aristotle’s opinion, that the size of the orifice of the hollow vein at the right chamber of the heart is greater than that of the body of the hollow vein, no matter where you measure the latter. Then the following chapter will show the falsity of Galen’s view that the hollow vein is largest at the point where it joins the hump of the liver.

As for Galen’s netlike plexus, I do not need to pass on a lot of misinformation about it here, as I am quite sure that I have examined the whole system of the cerebral vessels. There is no occasion for making things up, since we are certain that Galen was deluded by his dissection of ox brains and described the cerebral vessels, not of a human but of oxen.

Galen never inspected a human uterus.

How many things have been accepted on the word of Galen.

The great horde of physicians are always servile imitators, who can neither perceive nor correct the faults of their system, and are always ready to growl at and even to worry the ingenious person that could attempt it. Thus was the system of Galen secured in the possession of the schools of physic.

I realize that Galen called an earth which contained metallic particles a mixed earth when actually it is a composite earth. But it behooves one who teaches others to give exact names to everything.

Criticism of first principles which Aristotle and Ptolemy and Galen underwent waited longer in Euclid’s case than in theirs, it came for him at last. What Vesalius was to Galen, what Copernicus was to Ptolemy, that was Lobatchewsky to Euclid. There is, indeed, a somewhat instructive parallel between … Copernicus and Lobatchewsky.