Niko McCarty.@NikoMcCarty
In the early 1940s, there was intense debate about the “true nature” of bacteriophages, the little viruses that infect bacteria.
Some biologists argued that they were bacterial enzymes, whereas others believed they were their own viral entities.
In 1940, Ernst Ruska (the same person who invented the electron microscope in 1931), published an article in German showing the first images of a bacteriophage.
Ruska’s original electron microscope magnified objects only about 400x, much less than light microscopes available at that time. But by 1940, advances by University of Toronto scientists pushed that magnification up to 7,000x, or about 3x higher than light microscopes were then capable of.
Using one of these newer electron microscopes, Ruska captured his photos of bacteriophages. Unfortunately, the images were not so great. It was difficult to tell, for example, whether these were well-defined particles or just random debris from the bacterial cell. (Ruska’s image is the first one below.)
In 1942, two Americans — the brilliant Salvador Luria and Thomas Anderson, both at Columbia University — finally settled the debate.
Using a RCA Electron Microscope (of which only 2,000 units were ever made, each costing about $200,000) the two men acquired much better images of bacteriophages nestled upon a single E. Coli cell. (Their image is the second one below).
With this image, they could clearly see individual phages and their little tails. They saw, too, that these phages were of an “extremely constant and characteristic aspect,” meaning they could not just be random cell debris or enzymes (since the phages had two parts; heads and tails).
Their experiment worked like this: The duo dropped some phages on a tiny collodion film (made of cellulose, and thin enough not to distort the electron beams too much), put them into the machine, and then used a vacuum pump to suck air out of the column. (Without the vacuum, electrons would bounce off air particles and scatter.)
Next, they aligned the focus using a fluorescent screen on the front console. This fluorescent plate would convert the invisible electron image into visible light so the operator could see and tune the image live.
Finally, taking a micrograph involved opening a shutter for a second or two, then closing it and resetting the system for another shot. There was a long glass plate, at the bottom of the column, that caught the electrons which scattered off the phages. Each glass plate carried multiple small frames, so a session could produce several images before the plate had to be removed and developed in a darkroom.
It’s wild to me that these images were taken in the early 1940s; or that engineers were able to build these half-ton, ten-foot-tall machines that could blast biological samples and resolve their structures at such high resolutions. Brilliant.
