The cells which live naturally isolated in the organism, such as the corpuscles of the blood and spermatozoa, were the first studied. Since 1910 experiments on the survival of tissues have multiplied and at the same time more knowledge has been obtained concerning the conditions most favorable to survival and the microscopical appearances of the tissues so preserved. In 1910 Harrison, having placed fragments of an embryo frog in a drop of coagulated lymph taken from an adult, saw them continue their development for several weeks, the muscles and the epithelium differentiating, the nervous rudiments sending out into the lymph filaments similar to nerve fibers. Since 1910 with the aid of Dr. Minot, I have succeeded in preserving alive the nerve cells of the spinal ganglia of adult dogs and rabbits by placing them in defibrinated blood of the same animal, through which there bubbled a current of oxygen. At zero and perhaps better at 15°-20°, the structure of the cells and their colorable substance is preserved without notable change for at least four days; moreover, when the temperature is raised again to 39°, certain of the cells give a proof of their survival by forming new prolongations, often of a monstrous character. At 39° some of the ganglion cells which have been preserved rapidly lose their colorability and then their structure breaks up, but a certain number of the others form numerous outgrowths extremely varied in appearance. We have, besides, studied the influence of isotony, of agitation, and of oxygenation, and these experiments have enabled me to ascertain the best physical conditions required for the survival of nervous tissue. In 1910, Burrows, employing the technique of Harrison, obtained results similar to his with fragments of embryonic chickens. Since 1910 Carrel and Burrows applied the same method to what they call the "culture" of the tissues of the adult dog and rabbit; they have thus preserved and even multiplied cells of cartilage, of the thyroid, the kidney, the bone marrow, the spleen, of cancer, etc. Perhaps Carrel and his collaborators may be criticized for calling "culture" that which is merely a survival, but there still remains in their work a great element of real interest. Such are, too briefly summarized, the experiments which have been made up to the present time. We can readily imagine the practical consequences which we may very shortly hope to derive from them, and the wonderful applications of them which will follow in the domain of surgery. Without going so far as the dream of Dr. Moreau depicted by Wells, since grafts do not succeed between animals of different species, we may hope that soon, in many cases, the replacing of organs will be no longer impossible, but even easy, thanks to methods of conservation and survival which will enable us to have always at hand material for exchange. The dream of to-day may be reality to-morrow.