By use of suitable methods, different spots on the skin surface can be shown to be selectively sensitive to one of four sensory qualities in decreasing order of density: pain, touch, cool and warm. The presence of such spots was observed virtually simultaneously in the early 1880s by three independent investigators. Two papers on punctuate sensitivity of the skin were published in 1882 and 1883 by Magnus Blix of Uppsala University in Sweden; three papers were published in 1884 by Alfred Goldscheider, a German army doctor; and one was published in 1885 by Henry Donaldson of Johns Hopkins University in Maryland. Donaldson's findings originated from a serendipitous observation. In contrast, Blix's and Goldscheider's experiments were based on Johannes Muller's concept of "specific sense energies" and the extension of this idea to sensory qualities (the law of "specific nerve energies") by others, including Hermann von Helmholtz. The discovery of different types of sensory spots had considerable influence on other researchers of the period, including Max von Frey, but has only recently been substantiated by electrophysiological experiments.