One of three sailors, a black cook, has an idea to "rise cash." They sell his body as a corpse to a doctor. When the doctor goes to dissect the corpse it stands. The doctor runs to his wife, who bars the door and asks him to "leave off dissecting"
The shortage of cadavers for dissection which gave rise to this song is by no means exaggerated. Anatomists need bodies; so do beginning medical students. Robert M. Sapolsky, _The Trouble with Testosterone and Other Essays on the Biology of the Human Predicament_, Touchstone Books, 1997, pp. 117-119, notes the various problems the shortage of dead human bodies has caused. For starters, it gave rise to the occupation of the body snatcher -- people who went out and unearthed (often literally) the bodies of recently-dead people for use by doctors. It appears that the sailors in this song are imitating the snatchers.
There were two other sources of dead bodies: Executed criminals, and paupers. Henry VIII actually passed a law giving dead bodies of criminals to the doctors. These bodies at least were healthy, but they had suffered from execution -- and, before death, had suffered the brutal conditions of English prisons, and very likely from torture as well.
The corpses of the poor were intact, but these people had died of starvation, illness, and the general brutality of life. Their deaths were theoretically "natural," but they were usually hastened by their workhouse conditions.
The result was that doctors generally were not in position to examine the bodies of people who died of a healthy old age. Indeed, this remains a problem to this day, according to Sapolsky. It is a genuine problem both for doctors and for medical researchers -- he notes on p. 121 that two artificial diseases (one related to the adrenal glands and one related to the thymus) went into the diagnostic manuals as a result of always performing dissections on poor and sick people. The thymus problem was actually treated, with radiation, resulting in poorer health for those so treated plus a vast spike in cases of thyroid cancer (Sapolsky, p. 122). Under the circumstances, it is understandable that some doctors might be willing to work with the body snatchers. Ugly as their profession obviously was, it had the potential to bring good for many other people. - RBW