Hoc age ['do this'] is the great rule, whether you are serious or merry; whether ... learning science or duty from a folio, or floating on the Thames. Intentions must be gathered from acts.

Imprimisque hominis est propria veri inquisitio atque investigatio.
The first duty of man is the seeking after and the investigation of truth.

Les Leucocytes Et L'esprit De Sacrif1ce. — Il semble, d'après les recherches de De Bruyne (Phagocytose, 1895) et de ceux qui le citent, que les leucocytes des Lamellibranches — probablement lorsqu'ils ont phagocyté, qu'ils se sont chargés de résidus et de déchets, qu'ils ont, en un mot, accompli leur rôle et bien fait leur devoir — sortent du corps de l'animal et vont mourir dans le milieu ambiant. Ils se sacrifient. Après avoir si bien servi l'organisme par leur activité, ils le servent encore par leur mort en faisant place aux cellules nouvelles, plus jeunes.
N'est-ce pas la parfaite image du désintéressement le plus noble, et n'y a-t-il point là un exemple et un modèle? Il faut s'en inspirer: comme eux, nous sommes les unités d'un grand corps social; comme eux, nous pouvons le servir et envisager la mort avec sérénité, en subordonnant notre conscience individuelle à la conscience collective. (30 Jan 1896)
Leukocytes and The Spirit Of Sacrifice. - It seems, according to research by De Bruyne (Phagocytosis, 1885) and those who quote it, that leukocytes of Lamellibranches [bivalves] - likely when they have phagocytized [ingested bacteria], as they become residues and waste, they have, in short, performed their role well and done their duty - leave the body of the animal and will die in the environment. They sacrifice themselves. Having so well served the body by their activities, they still serve in their death by making room for new younger cells.
Isn't this the perfect image of the noblest selflessness, and thereby presents an example and a model? It should be inspiring: like them, we are the units of a great social body, like them, we can serve and contemplate death with equanimity, subordinating our individual consciousness to collective consciousness.

A story about the Jack Spratts of medicine [was] told recently by Dr. Charles H. Best, co-discoverer of insulin. He had been invited to a conference of heart specialists in North America. On the eve of the meeting, out of respect for the fat-clogs-the-arteries theory, the delegates sat down to a special banquet served without fats. It was unpalatable but they all ate it as a duty. Next morning Best looked round the breakfast room and saw these same specialists—all in the 40-60 year old, coronary age group—happily tucking into eggs, bacon, buttered toast and coffee with cream.

But nothing of a nature foreign to the duties of my profession [clergyman] engaged my attention while I was at Leeds so much as the, prosecution of my experiments relating to electricity, and especially the doctrine of air. The last I was led into a consequence of inhabiting a house adjoining to a public brewery, where first amused myself with making experiments on fixed air [carbon dioxide] which found ready made in the process of fermentation. When I removed from that house, I was under the necessity making the fixed air for myself; and one experiment leading to another, as I have distinctly and faithfully noted in my various publications on the subject, I by degrees contrived a convenient apparatus for the purpose, but of the cheapest kind. When I began these experiments I knew very little of chemistry, and had in a manner no idea on the subject before I attended a course of chymical lectures delivered in the Academy at Warrington by Dr. Turner of Liverpool. But I have often thought that upon the whole, this circumstance was no disadvantage to me; as in this situation I was led to devise an apparatus and processes of my own, adapted to my peculiar views. Whereas, if I had been previously accustomed to the usual chemical processes, I should not have so easily thought of any other; and without new modes of operation I should hardly have discovered anything materially new.

From whence it is obvious to conclude that, since our Faculties are not fitted to penetrate into the internal Fabrick and real Essences of Bodies; but yet plainly discover to us the Being of a GOD, and the Knowledge of our selves, enough to lead us into a full and clear discovery of our Duty, and great Concernment, it will become us, as rational Creatures, to imploy those Faculties we have about what they are most adapted to, and follow the direction of Nature, where it seems to point us out the way.

Her [Nightingale's] statistics were more than a study, they were indeed her religion. For her, Quetelet was the hero as scientist, and the presentation copy of his Physique Sociale is annotated by her on every page. Florence Nightingale believed—and in all the actions of her life acted upon that belief—that the administrator could only be successful if he were guided by statistical knowledge. The legislator—to say nothing of the politician—too often failed for want of this knowledge. Nay, she went further: she held that the universe—including human communities—was evolving in accordance with a divine plan; that it was man's business to endeavour to understand this plan and guide his actions in sympathy with it. But to understand God's thoughts, she held we must study statistics, for these are the measure of his purpose. Thus the study of statistics was for her a religious duty.

I believe scientists have a duty to share the excitement and pleasure of their work with the general public, and I enjoy the challenge of presenting difficult ideas in an understandable way.

I think it is a duty I owe to my profession and to my sex to show that a woman has a right to the practice of her profession and cannot be condemned to abandon it merely because she marries. I cannot conceive how women's colleges, inviting and encouraging women to enter professions can be justly founded or maintained denying such a principle.
(From a letter Brooks wrote to her dean, knowing that she would be told to resign if she married, she asked to keep her job. Nevertheless, she lost her teaching position at Barnard College in 1906. Dean Gill wrote that “The dignity of women's place in the home demands that your marriage shall be a resignation.”)

In my view, aiming at simplicity and lucidity is a moral duty of all intellectuals: lack of clarity is a sin, and pretentiousness is a crime.

It becomes the urgent duty of mathematicians, therefore, to meditate about the essence of mathematics, its motivations and goals and the ideas that must bind divergent interests together.

It is a right, yes a duty, to search in cautious manner for the numbers, sizes, and weights, the norms for everything [God] has created. For He himself has let man take part in the knowledge of these things ... For these secrets are not of the kind whose research should be forbidden; rather they are set before our eyes like a mirror so that by examining them we observe to some extent the goodness and wisdom of the Creator.

It is the business of the future to be dangerous; and it is among the merits of science that it equips the future for its duties.

No physiologist who calmly considers the question in connection with the general truths of his science, can long resist the conviction that different parts of the cerebrum subserve different kinds of mental action. Localization of function is the law of all organization whatever: separateness of duty is universally accompanied with separateness of structure: and it would be marvellous were an exception to exist in the cerebral hemispheres.

One of the first and foremost duties of the teacher is not to give his students the impression that mathematical problems have little connection with each other, and no connection at all with anything else. We have a natural opportunity to investigate the connections of a problem when looking back at its solution.

The advancement of science is slow; it is effected only by virtue of hard work and perseverance. And when a result is attained, should we not in recognition connect it with the efforts of those who have preceded us, who have struggled and suffered in advance? Is it not truly a duty to recall the difficulties which they vanquished, the thoughts which guided them; and how men of different nations, ideas, positions, and characters, moved solely by the love of science, have bequeathed to us the unsolved problem? Should not the last comer recall the researches of his predecessors while adding in his turn his contribution of intelligence and of labor? Here is an intellectual collaboration consecrated entirely to the search for truth, and which continues from century to century.
[Respecting how the work of prior researchers had enabled his isolation of fluorine.]

The largest land animal is the elephant, and it is the nearest to man in intelligence: it understands the language of its country and obeys orders, remembers duties that it has been taught, is pleased by affection and by marks of honour, nay more it possesses virtues rare even in man, honesty, wisdom, justice, also respect for the stars and reverence for the sun and moon.

The science of government is my duty. ... I must study politics and war that my sons may have liberty to study mathematics and philosophy. My sons ought to study mathematics and philosophy, geography, natural history, naval architecture, navigation, commerce, and agriculture, in order to give their children a right to study painting, poetry, music, architecture, statuary, tapestry, and porcelain.

The wise man should study the acquisition of science and riches as if he were not subject to sickness and death; but to the duties of religion he should attend as if death had seized him by the hair.

We cannot hope to build a better world without improving the individual. Toward this end, each of us must work for his own highest development, accepting at the same time his share of responsibility in the general life of humanity—our particular duty being to aid those to whom we think we can be most useful.

With moth cytochrome C there are 30 differences and 74 identities. With bread yeast and humans, there are about 45 amino acids that are different and about 59 that are identical. Think how close together man and this other organism, bread yeast, are. What is the probability that in 59 positions the same choice out of 20 possibilities would have been made by accident? It is impossibly small. There is, there must be, a developmental explanation of this. The developmental explanation is that bread yeast and man have a common ancestor, perhaps two billion years ago. And so we see that not only are all men brothers, but men and yeast cells, too, are at least close cousins, to say nothing about men and gorillas or rhesus monkeys. It is the duty of scientists to dispel ignorance of such relationships.