In her autobiography, Beverly Washburn says Patty Duke let her wear one of her own outfits for the scenes she appeared in.
Fin del mundo, which, as Martin ascertains, does mean 'end of the world' in Spanish. It is not, however, a town in Argentina. Ushuaia, the capital of Tierra del Fuego province in Argentina, often publicizes itself as the fin del mundo. While it is the southernmost town in Argentina, Puerto Williams in Chile is reputed to be even more southern geographically than Ushuaia.
Pellagra is a disease brought about by a deficiency of the vitamin B3, i.e. niacin.
This is the second of two appearances Mickey Deems makes in the series. In his first appearance, he affected a German accent, playing an eccentric German scientist in Patty, the Candy Striper (1965). Here, he plays a doctor and affects no accent other than a common American one.