But whilst Dr. Maurice Raynaud gave Pasteur the means of studying boils, Dr. Lannelongue enabled him to investigate that serious disease of the bones and marrow called 'osteomyelitis.' In February 1880 that skilful surgeon, who has published a highly esteemed work on osteomyelitis, and on the possibility of its cure by trepanning the bone, followed by washings and antiseptic dressings, conducted Pasteur to the Hospice Trousseau. A little girl twelve years of age, attacked with this cruel malady, was about to be operated upon. The right knee was much swollen, as was also all the leg to below the calf, and a part of the thigh above the knee. After having chloroformed the child, Dr. Lannelongue made a long incision below the knee, from which pus flowed abundantly. The bone of the tibia was laid bare for a considerable length. Three trepanning perforations were then made in the bone, from each of which the pus issued in great quantities. Pasteur carefully collected, with all the conditions necessary to the preservation of their purity, the pus of the exterior and the pus of the interior of the bone, and, returning to his laboratory, he examined them attentively. The direct observation, by a microscope, of the two specimens of pus was extremely interesting. It was obvious that they contained, in large quantities, an organism like that of boils, in pairs of two or four, and also in parcels, some with a clearly defined outline, others scarcely visible, and with very faint outlines. The external pus showed an abundance of pus globules, but that of the interior did not show any. It was like a paste entirely composed of microbes, so numerous and fertile that, in less than six hours after sowing them in the cultivating liquid, the development of the little microbe had commenced, and was rendered visible to the naked eye by a slight but general turbidity of the liquid. Its close resemblance to the organism of the boil might lead to the assertion that they are identical, if it were not known how great are the physiological differences that may exist between microscopic parasites of the same appearance and the same dimensions. I.