The fundamental principle of morality which we seek as a necessity for thought is not, however, a matter only of arranging and deepening current views of good and evil, but also of expanding and extending these. A man is really ethical only when he obeys the constraint laid on him to help all life which he is able to succor, and when he goes out of his way to avoid injuring anything living. He does not ask how far this or that life deserves sympathy as valuable in itself, nor how far it is capable of feeling. To him life as such is sacred. He shatters no ice crystal that sparkles in the sun, tears no leaf from its tree, breaks off no flower, and is careful not to crush any insect as he walks. If he works by lamplight on a summer evening, he prefers to keep the window shut and to breathe stifling air, rather than to see insect after insect fall on his table with singed and sinking wings.

The Animal World of Albert Schweitzer