Pyrex: construction, property, and uses in microbiology WORLD OF MICROBIOLOGY AND IMMUNOLOGY468•
re-directed to issues thought at one time to be dealt with and
no longer a concern.
Certain infectious diseases represent another increas-
ingly important public health issue. Just a few decades ago
AIDS was more of a curiosity, given its seeming confinement
to groups of people who were often marginalized and ostra-
cized. In the past decade, however, it has become clear that
AIDS is an all-inclusive disease. Aside from the suffering that
the illness inflicts, the costs of care for the increasingly debil-
itated and dependent patients will constitute a huge drain on
health care budgets in the decades to come. As a result, AIDS
research to develop an effective vaccineor strategies that pro-
long the vitality of those infected with the AIDS virus is a
major public health issue and priority.
Another public health issue of current importance is
chronic bacterial and viral diseases. Conditions like
fibromyalgia may have a bacterial or viral cause. The chronic
and debilitating Lyme diseasecertainly has a bacterial cause.
Moreover, the increasing use of surgical interventions to
enhance the quality of life, with the installation of heart pace-
makers, artificial joints, and the use of catheters to deliver and
remove fluids from patients, has created conditions conducive
for the explosion in the numbers of bacterial infections that
result from the colonization of the artificial surfaces. Such
bacterial biofilms have now been proven to be the source of
infections that persist, sometimes without symptoms, in spite
of the use of antibiotics. Such infections can be life threaten-
ing, and their numbers are growing. As with the other current
public health issues, chronic infections represent both a public
health threat and a budget drain.
A final area that has long been a public health concern
is the safety of food and water. These have always been sus-
ceptible to contaminationby bacteria, protozoaand viruses, in
particular. With the popularity of prepared foods, the monitor-
ing of foods and their preparation has become both more
urgent and more difficult for the limited number of inspectors
to do. Water can easily become contaminated. The threat to
water has become greater in the past twenty years, because of
the increasing encroachment of civilization on natural areas,
where the protozoan pathogens Giardiaand Cryptosporidium
normally live, and because of the appearance of more danger-
ous bacterial pathogens, in particular Escherichia coli
O157:H7. The latter organism is a problem in food as well.See alsoBacteria and bacterial infection; Epidemics and pan-
demics; Food safety; History of public health; Viruses and
responses to viral infectionPUBLIC HEALTH SYSTEMS•seeHISTORY OF
PUBLIC HEALTHPULSE-CHASE EXPERIMENT•seeLABORATORY
TECHNIQUES IN IMMUNOLOGYPYREX: CONSTRUCTION, PROPERTY,
AND USES IN MICROBIOLOGYPyrex: construction, property, and uses in microbiologyPyrex is a brand name of a type of glass that is constructed of
borosilicate. The Corning Glass Company of Corning, New
York, developed Pyrex. Chemically, as borosilicate implies,
this type of glass is composed of silica and at least five percent
(of the total weight of the elements in the glass) of a chemical
called boric oxide. The combination and concentrations of
these constituents confers great resistance to temperature
change and corrosion by harsh chemicals, such as strong acids
and alkalis, to whatever vessel is made of the borosilicate
glass. This durability has made Pyrex glassware extremely
useful in the microbiology laboratory.
The development of Pyrex in 1924 by scientists at the
Corning Company satisfied the demand for high quality scien-
tific glassware that had began in the nineteenth century. Then,
the glassware in existence was degraded by laboratory chemi-
cals and became brittle when exposed to repeated cycles of
heating and cooling. The formulation of Pyrex minimized the
tendency of the material to expand and contract. This main-
tained the accuracy of measuring instruments such as gradu-
ated cylinders, and overcame the brittleness encountered upon
repeated autoclave sterilizationof the laboratory glassware.
Pyrex glassware immediately found acceptance in the
microbiology research community. The popularity of the
glassware continues today, despite the development of heat
and chemical resistant plastic polymers. Glass is still the pre-
ferred container for growing bacteria. This is because the glass
can be cleaned using harsh chemicals, which will completely
remove any organic material that might otherwise adhere to
the sides of the vessel. For applications where the chemical
composition and concentrations of the medium components
are crucial, such organic contaminants must be removed.
Pyrex glassware is also used to manufacture graduated
cylinders that are extremely accurate. In some applications, the
exact volume of a liquid is important to achieve. This type of
glassware is known as volumetric glassware. Plastic still can-
not match the accuracy or the unchanging efficiency of volume
delivery that is achieved by Pyrex volumetric glassware.
Another application for borosilicate glass is in the meas-
urement of optical density. For this application, typically spe-
cially designed vials are filled with the solution or suspension
of interest and then placed in the path of a beam of light in a
machine known as a spectrophotometer. The amount of light
that passes through the sample can be recorded and, with the
inclusion of appropriate controls, can be used, for example, to
determine the number of bacteria in the sample. Plastic mate-
rial does not lend itself to optical density measurements, as the
plastic can be cloudy. Thus, the vial itself would absorb some
of the incoming light. Pyrex, however, can be made so as to be
optically transparent. Growth flasks have even been made in
which a so-called “side arm,” basically a test tube that is fused
onto the flask, can be used to directly obtain optical density
measurements without removing the culturefrom the flask.
In the same vein, the use of optically transparent slabs of
Pyrex as microscopeslides is a fundamental tool in the micro-womi_P 5/7/03 11:11 AM Page 468