Seeing Life Through the Microscope

The rapid spread of interest in microscopy in the 18th century spurred the development of tools for facilitating and improving the instrument's use. The examination of live frogs presented unique challenges, which instrument makers overcame in creative ways.

Johann Nathanael Lieberkühn, a German microscopist famous for his slide preparations, created a frog-plate much like Adams'. Both were made around 1740 for microscopic contemplation of living frogs. With built-in hooks on swivels, Lieberkühn's offered a more limited selection of positions in which to immobilize and prepare the frog than that of Adams, who preferred a system of taut strings rigged against his platform's brass frame.

Early microscopes lacked many conveniences that we enjoy today. For example, 18th century microscopists struggled to adequately illuminate their subjects, and the use of whole, living organisms compounded those difficulties. These frog plates pursue the same solution to that problem. Lieberkühn's plate features a small hole, where one could attach a microscope lens, which allowed background light to filter through and illuminate the frog's skin. Adams constructed his platform out of mesh wire rather than solid brass in order to exploit the frog's natural translucency.

Why were frogs popular subjects for these violent investigations, in spite of the difficulties they presented? From the 18th century until today, scientists have pointed to frogs' extraordinary ability to remain alive when kept in laboratory water tanks and to remain physiologically responsive even when their brains have been removed or their bellies cut open. The great Dutch naturalist and microscopist Jan Swammerdam noted in his Book of Nature (1738; English translation: 1758):

"There is scarce any animal which has the principle of life so strong as the Frog. It will continue moving many hours after the guts are taken out. An Eel is celebrated for this strength of life; but the Frog exceeds it greatly. No creature is so truly amphibious; for it will live for a length of time equally well on land without water, and absolutely immerged in water. A Frog has been tied down under water many days, and received no hurt, nor suffered any seeming inconvenience." (1)

References