Nicaise has emphasized the principles which guided Guy de Chauliac in the choice and interpretation of his authorities by a quotation from Guy himself, which is so different in its tone from what is usually supposed to have been the attitude of mind of the men of science of the time that it would be well for all those who want to understand the Middle Ages better to have it near them. Speaking of the surgeons of his own and immediately preceding generations, Guy says: "One thing particularly is a source of annoyance to me in what these surgeons have written, and it is that they follow one another like so many cranes. For one always says what the other says. I do not know whether it is from fear or from love that they do not deign to listen except to such things as they are accustomed to and as have been proved by authorities. They have to my mind understood very badly Aristotle's second book of metaphysics where he shows that these two things, fear and love, are the greatest obstacles on the road to the knowledge of the truth. Let them give up such friendships and fears. 'Because while Socrates or Plato may be a friend, truth is a greater friend.' Truth is a holy thing and worthy to be honored above everything else. Let them follow the doctrine of Galen, which is entirely made up of experience and reason, and in which one investigates things and despises words." After all, this is what great authorities in medicine have always insisted on. Once every hundred years or so one finds a really great observer who makes new observations and wakes the world up. He is surprised that men should not have used their powers of observation for themselves, but should have been following old-time masters. His contemporaries often refuse to listen to him at first. His observations, however, eventually make their way. We blame the Middle Ages for following authority, but what have we been always doing but following authority, except for the geniuses who come and lift us out of the rut and illuminate a new portion of the realm of medicine. After they have come, however, and done their work, their disciples proceed to see with their eyes and to think that they are making observations for themselves when they are merely following authority. When the next master in medicine comes along his discovery is neglected because men have not found it in the old books, and usually he has to suffer for daring to have opinions of his own. The fact of the matter is that at any time there is only a very limited number of men who think for themselves. The rest think other people's thoughts and think they are thinking and doing things. As for observation, John Ruskin once said, "Nothing is harder than to see something and tell it simply as you saw it." This is as true in science as in art, and only genius succeeds in doing it well.