Ruysch lectured with the help of specimens
To instruct in anatomy Ruysch preferred anatomical preparations above teaching from books.
He lectured publicly in the Anatomical Theater, for which he used fresh corpses. These lectures were intended for surgeons and in case the dead body happened to be female midwives were obliged to attend the anatomical lessons as well. Summer was not the correct time for dissecting corpses, as these rapidly decayed. But even in the wintertime it was not always easy for Ruysch to obtain an adequate corpse. A death sentence was not a daily occurrence and it did not often happen that someone died without family or relatives being present in the hospital. Apart from such public lessons he gave private lessons at his home. His specimens allowed him to demonstrate the framework of the human body throughout the year. Ruysch could prove explain particularities of the human anatomy to his fellow doctors, to his private medical students and to interested others.
Diseases and deformities
Ruysch collected in his cabinets mostly specimens depicting a normal, healthy anatomy, but he did posses a few aberrant specimens such as limbs and other parts of ill and deformed bodies. For instance, Thesaurus Anatomicus VI, Number 30, is a uterus with tumors. Occasionally Frederick Ruysch exhibits such a specimen from a diseased person next to a comparable one of a healthy person: two "cervix mouths" are shown as Numbers 85 and 86 in the same cabinet, a very narrow cervix (which according to Ruysch explains the woman's infertility) next to a normally sized specimen.
Number 81 is another exceptional specimen. It is a bottle containing a miscarried child that is only half a thumb long (a thumb being an old Dutch length measure, the extent of the distal phalanx of a male thumb), only half a month old, and connected to a sizeable placenta by a rather thick navel string. Ruysch accompanied this specimen with a warning in his catalogue: an early miscarriage accompanying a relatively large placenta may be partly due to coagulated blood. 'But', so he continues, 'the relatively large placenta is not an indication for a second child inside the uterus'. Ruysch warns medical students not to give women abortifacient medications to remove such a suspected second fetus in such a case.