Claude Bernard had begun by meditating deeply on the disease known as diabetes and which is characterized, as everybody knows, by a superabundance of sugar in the whole of the organism, the urine often being laden with it. But how is it, wondered Claude Bernard, that the quantity of sugar expelled by a diabetic patient can so far surpass that with which he is provided by the starchy or sugary substances which form part of his food? How is it that the presence of sugary matter in the blood and its expulsion through urine are never completely arrested, even when all sugary or starchy alimentation is suppressed? Are there in the human organism sugar-producing phenomena unknown to chemists and physiologists? All the notions of science were contrary to that mode of thinking; it was affirmed that the vegetable kingdom only could produce sugar, and it seemed an insane hypothesis to suppose that the animal organism could fabricate any. Claude Bernard dwelt upon it however, his principle in experimentation being this: “When you meet with a fact opposed to a prevailing theory, you should adhere to the fact and abandon the theory, even when the latter is supported by great authorities and generally adopted.”
This is what he imagined, summed up in a few words by Pasteur—
“Meat is an aliment which cannot develop sugar by the digestive process known to us. Now M. Bernard having fed some carnivorous animals during a certain time exclusively with meat, he assured himself, with his precise knowledge of the most perfect means of investigation offered him by chemistry, that the blood which enters the liver by the portal vein and pours into it the nutritive substances prepared and rendered soluble by digestion is absolutely devoid of sugar; whilst the blood which issues from the liver by the hepatic veins is always abundantly provided with it.... M. Claude Bernard has also thrown full light on the close connection which exists between the secretion of sugar in the liver and the influence of the nervous system. He has demonstrated, with a rare sagacity, that by acting on some determined portion of that system it was possible to suppress or exaggerate at will the production of sugar. He has done more still; he has discovered within the liver the existence of an absolutely new substance which is the natural source whence this organ draws the sugar that it produces.”
Pasteur, starting from this discovery of Claude Bernard’s, spoke of the growing close connection between medicine and physiology. Then, with his constant anxiety to incite students to enthusiasm, he recommended them to read the lectures delivered by Bernard at the Collège de France. Speaking of the Introduction to the Study of Experimental Medicine, Pasteur wrote: “A long commentary would be necessary to present this splendid work to the reader; it is a monument raised to honour the method which has constituted Physical and Chemical Science since Galileo and Newton, and which M. Bernard is trying to introduce into physiology and pathology. Nothing so complete, so profound, so luminous has ever been written on the true principles of the difficult art of experimentation.... This book will exert an immense influence on medical science, its teaching, its progress, its language even.” Pasteur took pleasure in adding to his own tribute praise from other sources. He quoted, for instance, J. B. Dumas’ answer to Duruy, who asked him, “What do you think of this great physiologist?” “He is not a great physiologist; he is Physiology itself.” “I have spoken of the man of science,” continued Pasteur. “I might have spoken of the man in everyday life, the colleague who has inspired so many with a solid friendship, for I should seek in vain for a weak point in M. Bernard; it is not to be found. His personal distinction, the noble beauty of his physiognomy, his gentle kindliness attract at first sight; he has no pedantry, none of a scientist’s usual faults, but an antique simplicity, a perfectly natural and unaffected manner, while his conversation is deep and full of ideas....” Pasteur, after informing the public that the graver symptoms of Bernard’s disease had now disappeared, ended thus: “May the publicity now given to these thoughts and feelings cheer the illustrious patient in his enforced idleness, and assure him of the joy with which his return will be welcomed by his friends and colleagues.”
The very day after this article reached him (November 19, 1860) Bernard wrote to Pasteur: “My dear friend,—I received yesterday the Moniteur containing the superb article you have written about me. Your great praise indeed makes me proud, though I feel I am yet very far from the goal I would reach. If I return to health, as I now hope I may do, I think I shall find it possible to pursue my work in a more methodical order and with more complete means of demonstration, better indicating the general idea towards which my various efforts converge. In the meanwhile it is a very precious encouragement to me to be approved and praised by a man such as you. Your works have given you a great name, and have placed you in the first rank among experimentalists of our time. The admiration which you profess for me is indeed reciprocated; and we must have been born to understand each other, for true science inspires us both with the same passion and the same sentiments.
“Forgive me for not having answered your first letter; but I was really not equal to writing the notice you wanted. I have deeply felt for you in your family sorrow; I have been through the same trial, and I can well understand the sufferings of a tender and delicate soul such as yours.”
Henri Sainte Claire Deville, who was as warm-hearted as he was witty, had, on his side, the ingenious idea of editing an address of collective wishes for Claude Bernard, who answered: “My dear friend,—You are evidently as clever in inventing friendly surprises as in making great scientific discoveries. It was indeed a most charming idea, and one for which I am very grateful to you—that of sending me a collective letter from my friends. I shall carefully preserve that letter: first, because the feelings it expresses are very dear to me; and also because it is a collection of illustrious autographs which should go down to posterity. I beg you will transmit my thanks to our friends and colleagues, E. Renan, A. Maury, F. Ravaisson and Bellaguet. Tell them how much I am touched by their kind wishes and congratulations on my recovery. It is, alas, not yet a cure, but I hope I am on a fair way to it.
“I have received the article Pasteur has written about me in the Moniteur; that article paralysed the vasomotor nerves of my sympathetic system, and caused me to blush to the roots of my hair. I was so amazed that I don’t know what I wrote to Pasteur; but I did not dare say to him that he had wrongly exaggerated my merits. I know he believes all that he writes, and I am happy and proud of his opinion, because it is that of a scientist and experimentalist of the very first rank. Nevertheless, I cannot help thinking that he has seen me through the prism of his kindly heart, and that I do not deserve such excessive praise. I am more than thankful for all the marks of esteem and friendship which are showered upon me. They make me cling closer to life, and feel that I should be very foolish not to take care of myself and continue to live amongst those who love me, and who deserve my love for all the happiness they give me. I intend to return to Paris some time this month, and, in spite of your kind advice, I should like to take up my Collège de France classes again this winter. I hope to be allowed not to begin before January. But we shall talk of all this in Paris. I remain your devoted and affectionate friend.”
To end this academic episode, we will quote from Joseph Bertrand’s letter of thanks to Pasteur, who had sent him the article: “...The public will learn, among other things, that the eminent members of the Academy admire and love each other sometimes with no jealousy. This was rare in the last century, and, if all followed your example, we should have over our predecessors one superiority worth many another.”
Thus Pasteur showed himself a man of sentiment as well as a man of science; the circle of his affections was enlarging, as was the scope of his researches, but without any detriment to the happy family life of his own intimate circle. That little group of his family and close friends identified itself absolutely with his work, his ideas and his hopes, each member of it willingly subordinating his or her private interests to the success of his investigations. He was at that time violently attacked by his old adversaries as well as his new contradictors. Pouchet announced everywhere that the question of spontaneous generation was being taken up again in England, in Germany, in Italy and in America. Joly, Pouchet’s inseparable friend, was about to make some personal studies and to write some general considerations on the new silkworm campaign. Pasteur, who had confidently said, “The year 1867 must be the last to bear the complaints of silkworm cultivators!” went back to Alais in January, 1867. But, before leaving Paris, Pasteur wrote out for himself a list of various improvements and reforms which he desired to effect in the administration of the Ecole Normale, showing that his interest in the great school had by no means abated, in spite of his necessary absence. He brought with him his wife and daughter, and Messrs. Gernez and Maillot; M. Duclaux was to come later. The worms hatched from the eggs of healthy moths and those from diseased ones were growing more interesting every day; they were in every instance exactly what Pasteur had prophesied they would be. But besides studying his own silkworms, he liked to see what was going on in neighbouring magnaneries. A neighbour in the Pont Gisquet, a cultivator of the name of Cardinal, had raised with great success a brood originating from the famous Japanese seed. He was disappointed, however, in the eggs produced by the moths, and Pasteur’s microscope revealed the fact that those moths were all corpuscled, in spite of their healthy origin. Pasteur did not suspect that origin, for the worms had shown health and vigour through all their stages of growth, and seemed to have issued from healthy parents. But Cardinal had raised another brood, the produce of unsound seed, immediately above these healthy worms. The excreta from this second brood could fall on to the frames of those below them, and the healthy worms had become contaminated. Pasteur demonstrated that the pébrine contagion might take place in one or two different ways: either from direct contact between the worms on the same frame, or by the soiling of the food from the very infectious excreta. The remedy for the pébrine seemed now found. “The corpuscle disease,” said Pasteur, “is as easily avoided as it is easily contracted.” But when he thought he had reached his goal a sudden difficulty rose in his way. Out of sixteen broods of worms which he had raised, and which presented an excellent appearance, the sixteenth perished almost entirely immediately after the first moulting. “In a brood of a hundred worms,” wrote Pasteur, “I picked up fifteen or twenty dead ones every day, black and rotting with extraordinary rapidity.... They were soft and flaccid like an empty bladder. I looked in vain for corpuscles; there was not a trace of them.”