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In April 1897, Oswaldo Cruz and his family set sail for Paris, where he would continue his studies. His destination was the Pasteur Institute, then the world’s foremost center of microbiology.

When he arrived in the French capital, Cruz intended to start his program of studies in microbiology as soon as possible. However, his obligations as a family man and his need to earn a living were more pressing. Cruz had been warned by his friends and so was well aware of the hardships a young physician would face if he tried to live solely off laboratory research. He was forced to practice medicine as well—and it would be best if he had a specialty.

It was no doubt with this in mind that he decided to contact Prof. Félix Guyon right after he got to Paris. Prof. Guyon had a urology practice. Venereal diseases were spreading quickly and were the main reason people sought out doctor’s offices in the late nineteenth century, so the field was one of the most promising.

At the Pasteur Institute, Cruz was received by the scientist Émile Roux, who was to become his friend. Cruz also received good news upon his arrival: he had been given a special exemption and, unlike other students, would not need to pay for the materials and lab animals he would use in his research. When Cruz asked why he had been singled out like this, he was informed that it was in recognition of the contributions that former Emperor Dom Pedro II had made to help found the Pasteur Institute.

The French scientist Louis Pasteur had died two years earlier, so Cruz never met him, but he did have the good fortune of studying with the first generation of Pasteurians. In addition to Roux (Technical Microbiology), this included Émile Duclaux (General Microbiology); Charles Chamberland (Microbiology Applied to Hygiene); Elie Metchnikoff (Morphological Microbiology), and Joseph Grancher (Rabies Service), all of whom had made noteworthy contributions to science and experimental medicine.

While studying at the institute, Cruz began an internship at the Toxicology Laboratory of Paris, headed by Charles Vibert and Jules Ogier. He strove to learn all he could from them about the practice of forensic medicine, an area that often relies on toxicology studies.

Despite his very busy schedule, Cruz still found time to learn how to make glass lab equipment at a factory. Laboring alongside the factory workers, he learned to make everything needed to equip a research laboratory: vials, pipettes, beakers, test tubes—he overlooked nothing in his learning experience. Cruz was to introduce this technology to Brazil and was the first in the country to produce vials. Years later, he established a special section for this purpose at the Federal Serum Therapy Institute.

Cruz stayed in Paris for about two years and three months. A number of papers came out of his research, published in Portuguese, French, and Italian. In mid-1899, with his studies completed, he returned to Brazil.