The technique was introduced into histology by Liesegang28 primarily as a new silver staining technique for impregnation of tissue sections, and he used the photographic term physical development for the process. Later, the term autometallography was suggested.12 Liesegang also tried to trace silver in exposed animals by silver enhancement, but failed.29 Roberts was more successful in observing a difference in the number of silver grains among tissue sections from animals treated with gold salts and from control animals.44 His work was followed by several important attempts to trace gold in exposed tissues,43 but it was not until Timm’s introduction of his

famous sulfide silver method in 1958 and his mercury method in 196259,60 that the field really gained scientific momentum and began to expand. Timm’s two methods have since proved very valuable and successful. They have resulted in a multitude of publications and have been subjected to a wealth of technical modifications.