Frogs and Physiological Instruments in 20th Century Cambridge

This page explores the history of the Cambridge Department of Physiology, focussing on two reccurring themes: frequent collaborations with instrument manufacturers, and a reliance on "the physiologist's little friend the frog," as A.V. Hill once described it, as a research specimen. The foundation of the Department created a demand for physiological instruments and thus a demand for a local instrument company. The Cambridge Scientific Instrument Company, created in 1881, addressed this need.

Early Cambridge Physiology and the Cambridge Scientific Instrument Company

In the 19th century, the University of Cambridge was notorious for its conservatism toward science. It finally responded to calls for change by founding three scientific institutions in the 1870s: the Cavendish Laboratory, the Department of Mechanism and Applied Mechanics, and the Physiological Laboratory. This created a large, pressing demand for a variety of scientific instruments, but the departments' in-house instrument makers were unable to completely satisfy their needs. The crisis was resolved in 1881 with the foundation of the Cambridge Scientific Instrument Company (CSIC).

In its early years, most of the Company's business was generated by the Department of Physiology. Sir Michael Foster (the founder of the Department and the compiler of our Foster Collection) and his students sometimes collaborated with CSIC to create and improve instruments for their experiments on frogs. For instance, the Company commercially produced two frog cardiographs, each designed by one of Foster's former students. One of these men, Walter Holbrook Gaskell, used his frog cardiograph to make crucial discoveries, including the path of electrical conduction through the heart.

Cambridge physiologists continued to collaborate with CSIC for the entirety of its existence, but the scientist with the closest links to the Company was Keith Lucas (1879-1916). Lucas served both as a Trinity College lecturer in Natural Sciences and as a CSIC board member. He was an extremely skilled instrument designer, and the Company commercially produced several devices that he had originally custom-made for his own experiments on frogs. One of these is the Lucas Pendulum, which could open successive electrical circuits for short periods of time, thus stimulating a nerve or muscle. The Whipple Museum holds two CSIC Lucas Pendulums: Wh.5000 (1907) and Wh.4133 (1938). The production date of Wh. 4133 reveals that Lucas' pendulum was so excellent that it was sold for over thirty years with only minimal changes to its design.

Though Lucas' instruments could be used with multiple species, he described frog vivisections in all twenty-three articles that he published in the Journal of Physiology. In his only paper that was not dedicated to frog research, Lucas still used frog muscle, because he was so familiar with it, to calibrate his apparatus before beginning his actual experiments on crayfish.

The Whipple Museum takes its name from Robert Stewart Whipple (1871-1953) who presented his collection of 1000 scientific instruments, and a similar number of rare books, to the University in 1944.

Seeing Frogs in New Ways: Sir Andrew Huxley and Interference Microscopy

Like several of his predecessors in the Cambridge Department of Physiology, Sir Andrew Huxley (1917-2012) conducted experiments on frogs that yielded important physiological discoveries. Huxley's lifelong passions for mechanical engineering and microscopy served him well in his career as a physiologist, which often required the creation of custom pieces of apparatus. He designed his interference microscope to perceive the anatomy and physiology of frog muscles in a new way, which led to his postulation of the sliding filament model of muscle contraction.

Huxley hoped that studying changes in muscle fibres' striation patterns could provide insight into the mechanics of muscle contraction. He decided to use frog skeletal muscle due to the regularity of its structure and its easy excitability. Unfortunately, however, the striations in frog muscle were too narrow to be observed via ordinary light microscopy, and the frog muscle fibres were too thick to be observed via phase contrast. Huxley's options were further restricted because the phenomenon did not appear in polarised light. He realised that he could perceive the striations in frog muscles if he built an interference microscope and collaborated with the London instrument manufacturer R & J. Beck Limited to design one.

Huxley's basic design paired a standard polarising microscope with two Wollaston prisms, which divided light into two sections and then recombined the beams. This allowed the striations to be viewed and photographed. After a year of experimentation using the interference microscope and frog muscles, Huxley and his collaborator Rolf Niedergerke developed the sliding filament model of muscle contraction. This states that the sarcomeres in skeletal muscles are composed of thin and thick filaments, and during contraction, the former slide past the latter.

Huxley was concerned that his theory would not be accepted unless his results were replicated. The best way to ensure this, he reasoned, would be for his microscope itself to be reproduced, but his attempts to have it commercially produced ended in failure due to a pre-existing patent on a similar interference microscope. The sliding filament theory, to Huxley's surprise, was actually quickly accepted by the scientific majority because it was independently and simultaneously postulated by Hugh Huxley (no relation to Andrew) and Jean Hanson. The fact that they had used both a different instrument (an electron microscope) and a different animal (the rabbit) and yet created the same theory served as persuasive evidence of its veracity.

Just as experiments with other microscopes and species could provide validation for Huxley's claims, so too could they yield challenges. Physiologist James Duncan Robertson used lizards to generate results that contradicted observations that Huxley had recently made using a polarising microscope. Had one man or the other erred, or did their contradictory results stem from an inherent difference between frogs and lizards? To settle the debate, Huxley repeated his experiments but with different instruments: his interference microscope and a new adjunct apparatus that he had invented, a ribbon filament lamp (Wh.6574). He used frogs again, but also experimented on crabs and lizards. He got the same (original) result in all three species, proving that he had been correct.