"Bacterial Fingerprints"

The article presents information on the curious occurrence of identifiable fingerprints outlined in bacterial colonies. As an experiment in the study of the bacterial flora of the skin, the thumb was sweated in a moist, warm chamber and then pressed gently upon the surface of a nutrient agar plate three successive times. The plate was then incubated to grow the bacteria, with the result shown in the accompanying illustration. Only the first impression resulted in an entire and identifiable fingerprint; the second is a fragmentary impression containing only a few fingerprint ridges, and the third shows no pattern traces at all. The physician reports that the clearly formed design of the first impression is composed of small pinpoint colonies derived from bacteria normally living in the deeper parts of the cornified layer of the skin and can be demonstrated only by the type of experiment described, in which the cornified layer becomes swollen and spongy as in the familiar "wash-woman's hand."