he had to deal with was the bubonic plague, which is recognizable most of the time through the abscesses, known as buboes, it provokes in its victims. Yersin looked for the germ responsible for the infection specifically in these plague spots, tumors caused by the inflammation of the lymphatic glands which become black because of the necrosis of the tissue. After many microscopic exams he was able to state that in most of the cases the bubonic plague bacterium was located in these buboes; but in the meanwhile, the Japanese scientist Kitasato also declared that he had isolated the bacterium, even though the description he provided differed from the one given by Yersin. Therefore, although at first named "Kitasato-Yersin bacillus" by the scientific community, the microbe would later be called by the latter's name because the one identified by Kitasato, a type of streptococcus, cannot be found in the lymphatic glands. However it was Paul-Louis Simond who was the first to understand and describe the etiology of the plague and its modality of contamination: he observed small flea-bites on the bodies of the people affected by it, which he also found on the bodies of the dead rats that were linked to the plague, and then deduced that the fleas which carried the bacteria were its true vector or source, and that they transmitted the illness by jumping from the dead rats' bodies to the human ones and biting them. Calmette's and Guerin's anti-tuberculosis vaccine By the beginning of the 20th century, improvement of living conditions and development of a more extensive conception of hygiene produced a slight regression in tuberculosis cases in France: nonetheless the institute's labs, like many other ones, kept trying to find among the Koch's bacillus many singularities the one that would allow them to find an antidote. Right after he had discovered the bacillus, Koch had tried in vain to create a vaccine against it, however, the injection of the filtrate he had prepared, later called tuberculin, had the effect of revealing who was phthisic from who was not by causing in the latter—and not in the former—fever and light trembling. The institute's newspaper was filled at the time with articles regarding tuberculosis, some of which were written by Albert Calmette, who extended his research to a socio-professional category which was extremely affected by it, that is the miners in whom this disease is often