“Just as the supposed number may differ from the true number by fully 100, 150, or even 200 in a flock of 600 sheep, so may I be even more out of my reckoning in the case of these very little animalcules.”

I saw this vast number of animalcules not all through the semen, but only in the liquid matter adhering to the thicker part.

Examining this water…I found floating therein divers earthy particles, and some green streaks, spirally wound serpent-wise.

My determination is not to remain stubbornly with my ideas, but I’ll leave them and go over to others as soon as I am shown plausible reasons which I can grasp.

In the year 1657 I discovered very small living creatures in rain water.

I’ve never taught one, because if I taught one, I’d have to teach others. I would give myself over to a slavery, whereas I want to stay a free man.

How inscrutable and incomprehensible are the hidden works of Nature!

How little do we discover in comparison of those things which now are and forever will be hidden from our sight? The whole of which I am fully persuaded no one will ever be able to dive into, and to explain their causes and effects.

Man comes not from an egg but from an animalcule that is found in male sperm.

Man has always to be busy with his thoughts if anything is to be accomplished.

I’ve spent more time than many will believe [making microscopic observations], but I’ve done them with joy, and I’ve taken no notice those who have said why take so much trouble and what good is it?

I have often endeavoured to view the circulation of the blood in terrestrial animals, but without success, by reason that no parts of their bodies were sufficiently transparent.

For my part, I would say that the male sperm and seeds of plants have been penetrated so far that there is nothing further to discover in this great secret, but I could err in my opinion.

I have divers times endeavoured to see and to know, what parts the Blood consists of; and at length I have observ’d, taking some Blood out of my own hand, that it consists of small round globuls driven through a Crystalline humidity or water.

In rain water, I observed a small red worm and two other kinds of very minute insects; of those of the larger size, I judged that 30,000 together would not equal a coarse sand.

I have oft-times been besought, by divers gentlemen, to set down on paper what I have beheld through my newly invented microscopia, but I have generally declined.

For my part, I hold it equally impossible for a small shellfish to be produced without generation as for a whale to have its origin from the mud.

All the animals, the plants, the minerals, even other kinds of men, are being broken and reassembled every day, to preserve an elite few, who are the loudest to theorize on freedom, but the least free of all.

There is not in the universe a more ridiculous, nor a more contemptible animal, than a proud clergyman.

What is the Law of the Jungle? Strike first and then give tongue.

We are the storytelling animal.

My great forte in killing buffaloes was to get them circling by riding my horse at the head of the herd and shooting their leaders. Thus the brutes behind were crowded to the left, so that they were soon going round and round.

Thirst teaches all animals to drink, but drunkenness belongs only to man.

Be more than man, or thou’rt less than an ant.

I can say with sincerity that I like cats. A cat is an animal which has more human feelings than almost any other.