The Science Book

197

This electron micrograph image

shows particles of the tobacco mosaic

virus at 160,000x magnification.

The particles have been stained

to enhance their visibility.

See also: Friedrich Wöhler 124–25 ■ Louis Pasteur 156–59 ■ Lynn Margulis 300–01 ■ Craig Venter 324–25

A CENTURY OF PROGRESS

for the tobacco industry. His results
led him to apply the term virus—
already in occasional use for
substances that were toxic or
poisonous—to the contagious
agents that caused the disease.
At the time, most of Beijerinck’s
contemporaries in science and
medicine were still grappling with
understanding bacteria. Louis
Pasteur and German physician
Robert Koch had first isolated and
identified them as disease-causing
in the 1870s, and more were being
discovered constantly.
A common method of testing
for bacteria at the time was to pass
liquid containing the suspected
contagions through various sets of
filters. One of the best known was
the Chamberland filter, invented in
1884 by Pasteur’s colleague Charles
Chamberland. It used minute pores
in unglazed porcelain to capture
particles as small as bacteria.

Too small to filter
Several researchers had suspected
that there was a class of infectious
agents even tinier than bacteria

that could pass on disease. In 1892,

Russian botanist Dmitri Ivanovsky

performed tests on tobacco mosaic

disease, showing that its infection

agent passed through the filters.

He established that the agent in

this case could not be bacteria,

but did not investigate further to

discover what the agent might be.

Beijerinck repeated Ivanovsky’s

experiment. He, too, established

that even after juice pressed from

the leaves was filtered, tobacco

mosaic disease was still present.

Indeed, at first he thought that the

cause was the fluid itself, which he

called contagium vivum fluidium

(contagious living fluid). He further

demonstrated that the contagion

carried in the fluid could not be

grown in laboratory nutrient gels

or broths, nor in any host organism.

It had to infect its own specific

living host in order to multiply

and spread the disease.

Even though viruses could not

be seen by light microscopes of

the time, grown with the usual

laboratory culture methods, or

detected by any of the standard

microbiological techniques,

Beijerinck figured out that they

really did exist. He insisted that

they caused disease, propelling

microbiology and medical science

into a new era. It would not be

until 1939, with the aid of electron

microscopes, that tobacco mosaic

virus became the first virus to have

its photograph taken. ■

Martinus Beijerinck Something of a recluse, Martinus

Beijerinck spent many solitary

hours experimenting in the

laboratory. He was born in

Amsterdam in 1851, and studied

chemistry and biology in Delft,

graduating in 1872 from Leiden

University. Focusing on soil and

plant microbiology at Delft, he

performed his famous filtering

experiments on the tobacco

mosaic virus in the 1890s. He

also studied how plants capture

nitrogen from the air and

incorporate it into their tissues—

a kind of natural fertilizer system

that enriches the soil—as well

as working on plant galls,

fermentation by yeasts and

other microbes, the nutrition of

microbes, and sulfur bacteria.

By the end of his life, he was

internationally recognized. The

Beijerinck Virology Prizes, set up

in 1965, are awarded every two

years in the field of virology.

Key works

1895 On Sulphate Reduction by

Spirillum desulfuricans

1898 Concerning a contagium

vivum fluidium as a Cause of the

Spot-disease of Tobacco Leaves