Lusitano has been credited with early recognition of the circulation of the blood. How much he might have understood the circulation remains in doubt; however, through dissections of the Azygos vein, he was the first to observe and record his observations of the venous valves.
In Centuria I, paragraph (Curatio) 513 Lusitano described how, in 1547, he performed an experiment before some scholars from the University of Ferrara, blowing air into the lower part of the azygos, and showing that the vena cava would not be inflated. It was not possible for the air to escape because of the valve or operculum mentioned. The anatomist Giambattista Canano, witnessed these experiments, and discovery of the valves was later attributed to him by mistake.

Of 16th century Jewish physicians, Lusitano may have been the most significant in terms of the number of his scientific contributions and the extent of his publications.

Digital facsimile from Google Books at this link.

Contains (Cent. iii, curat. 70, p. 286) first recorded case of purpura as a separate entity, not associated with fever. English translation of this section in Major, Classic descriptions of disease, 3rd. ed., 1945, p. 514.

The first treatise on gynecology written by a Portuguese author, the work was written in two parts: Part one, about theory, was titled De natura mulierum (On female nature) and was divided into four books: (1) Anatomy of the uterus and the breasts; (2) Semen and menstruation; (3) Intercourse, conception, and pregnancy; (4) Childbirth and breastfeeding. Part two, titled De morbis mulierum (On female diseases) was more practical in nature, but was also divided into four books: (1) Diseases common to all women; (2) Diseases of widows and virgins; (3) Diseases related to generation and pregnancy; (4) Puerperal and wetnurses’ diseases.

In exploring issues in physiology and anatomy, embryology, conception, sex, pregnancy, abortion, infertility, childbirth, monstrous beings, etc de Castro evaluated classical and Arabic traditional thinking on these subjects in the writings of Hippocrates, Aristotle, Pliny, Soranus, Galen, Averroes, Avicenna, etc., He also established a multivocal dialogue between traditional ideas and new ideas, engaging with the work of more contemporary authors such as Du Laurens, Amato Lusitano, Mercado, Akakia, Paré, Rousset, Mercuriale and others. 

Digital facsimile of the 1604 edition from Google Books at this link.

One of the first “modern” works on medical ethics. Digital facsimile from Google Books at this link.