Tout est poison, rien n'est poison, tout est une question de dose.
Everything is poisonous, nothing is poisonous, it is all a matter of dose.

A barbarous practice, the inconsistency, folly, and injury of which no words can sufficiently describe.
Condemning the use of mercurial medicines.

He, who for an ordinary cause, resigns the fate of his patient to mercury, is a vile enemy to the sick; and, if he is tolerably popular, will, in one successful season, have paved the way for the business of life, for he has enough to do, ever afterward, to stop the mercurial breach of the constitutions of his dilapidated patients. He has thrown himself in fearful proximity to death, and has now to fight him at arm's length as long as the patient maintains a miserable existence.

If you could see what I almost daily see in my practice … persons … in the very last stages of wretched existence, emaciated to a skeleton, with both tables of the skull almost completely perforated in many places, half the nose gone, with rotten jaws, ulerated throats, breaths most pestiferous more intolerable than poisonous upas, limbs racked with the pains of the Inquisition, minds as imbecile as the puling babe, a grievous burden to themselves and a disgusting spectacle to others, you would exclaim as I have often done, 'O! the lamentable want of science that dictates the abuse (use) of that noxious drug calomel!'
[Calomel is the mercury compound, Hg₂Cl₂.]

In 1810, the Triumph man-of-war and Phipps schooner received on board several tons of quicksilver, saved from the wreck of a vessel near Cadiz. In consequence of the rolling of the bags the mercury escaped, and the whole of the crews became more or less affected. In the space of three weeks, two hundred men were salivated, two died, and all the animals—cats,dogs,sheep,fowls,a canary bird, nay, even the rats, mice and cockroaches'were destroyed.
[The leather bags of mercury had been salvaged and stored without the original wooden cases. Some were stowed in sleeping quarters, and the in same hold as spirit rations.]

Poison should be tried out on a frog.

The American is a gentle guy; but don't pressure him; if you do he turns toad and squirts poison.

This [cyanide] poison is for professors of chemistry only. You, as a professor of mechanics, will have to use the rope.
Said during the Nazi occupation of Norway.

We starve the rats, creosote the ticks, swat the flies, step on the cockroaches and poison the scales. Yet when these pests appear in human form we go paralytic.

Why Become Extinct? Authors with varying competence have suggested that dinosaurs disappeared because the climate deteriorated (became suddenly or slowly too hot or cold or dry or wet), or that the diet did (with too much food or not enough of such substances as fern oil; from poisons in water or plants or ingested minerals; by bankruptcy of calcium or other necessary elements). Other writers have put the blame on disease, parasites, wars, anatomical or metabolic disorders (slipped vertebral discs, malfunction or imbalance of hormone and endocrine systems, dwindling brain and consequent stupidity, heat sterilization, effects of being warm-blooded in the Mesozoic world), racial old age, evolutionary drift into senescent overspecialization, changes in the pressure or composition of the atmosphere, poison gases, volcanic dust, excessive oxygen from plants, meteorites, comets, gene pool drainage by little mammalian egg-eaters, overkill capacity by predators, fluctuation of gravitational constants, development of psychotic suicidal factors, entropy, cosmic radiation, shift of Earth's rotational poles, floods, continental drift, extraction of the moon from the Pacific Basin, draining of swamp and lake environments, sunspots, God's will, mountain building, raids by little green hunters in flying saucers, lack of standing room in Noah's Ark, and palaeoweltschmerz.

[Mercurial medicines] affect the human constitution in a peculiar manner, taking, so to speak, an iron grasp of all its systems, and penetrating even to the bones, by which they not only change the healthy action of its vessels, and general structure, but greatly impair and destroy its energies; so that their abuse is rarely overcome. When the tone of the stomach, intestines, or nervous system generally, has been once injured by this mineral ... it could seldom be restored.