Vaccari D.A., Strom P.F., Alleman J.E. Environmental Biology for Engineers and Scientists

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12.7.8 Hepatitis B

Hepatitis B, or serum hepatitis, is spread mainly through contaminated blood, often

from unsterilized needles shared by drug users or used for tattoos or ear or body piercing.

The virus can also be transmitted sexually. Over 100,000 people are infected yearly in the

United States, but this number is decreasing due to the recent introduction of a vaccine. In

addition to the initial disease, which is more severe than hepatitis A (more liver damage

and fatality rate of 10%), those infected are at higher risk of liver cancer.

12.7.9 Ebola

The index (ﬁrst noted) case for the Ebola virus took place in Zaire in 1976, with more

than 300 victims of this severe hemorrhagic (bleeding) fever. A second outbreak in

Sudan killed another 150 people, and other, usually smaller outbreaks have since been

reported, mainly in east, central, and southern areas of Africa. Ebola virus spreads through

the body, with rapid necrosis (death) of cells in the infected organs, particularly those of

the liver, lymph system, kidneys, ovaries, and testes. Patients usually have sustained high

fevers and may become delirious and difﬁcult to control. After about a wee k, profuse

bleeding occurs throughout the body, and 90% of patients die.

It is believed that animals, including monkeys and perhaps also bats, are the main

reservoir for the virus. Ebola outbreaks result from person-to-person transmission invol-

ving close contact, probably with infected blood or other ﬂuids, although the exact route

of transmission is unknown. Unfortunately, nosocomial spread typically occurs before the

disease is recognized, and hospital staff membe rs are often among the early victims.

12.8 CONTROL OF INFECTION

A variety of methods have been used to help prevent the spread of disease. These involve a

variety of physical steps taken outside the human b ody to prevent transmission, ways to

make a person immune to a disease, and chemicals administered to control a microbial

agent or its products once they are inside a host.

12.8.1 Physical Steps to Prevent Transmission

General sanitation is an important step in preventing transmission of many diseases.

Proper disposal of sewage and adequate treatment of potable water, including ﬁltration

and disinfection, have gone a long way to limit waterborne disease in many areas. Ade-

quate cooking, proper refrigeration, and thorough handwashing have been important steps

in controlling foodborne outbreaks. Pasteurization (heat treatment to kill pathogens) or

complete sterilization (killing all microorganisms) of milk and many other foods has also

had a major role in reducing disease. Vector control has been effective for many diseases,

and pesticides, despite their potential other risks, certainl y have played an important role

in this regard. Use of condoms reduces the risk of spreading sexually transmitted diseases.

Sterile surgical equipment, bandages, and other hospital equipment and supplies and the

use of surgical masks and gloves has greatly reduced infections from medical procedures.

Quarantine (forced isolation of infectious persons) still plays an important role in

the control of some diseases. These are only a few examples of physical changes in the

378 EFFECT OF MICROBES ON HUMAN HEALTH

environment that can help in controlling disease transmission. Maintaining a healthy, nor-

mal microbial biota in and on the body can also help prevent invasion by a pathogen.

12.8.2 Immunity and Vaccination

Immunity (the ability to resist infection based on mobilization of the immune system) to

many diseases can result from a prior infection of the same agent. Getting the measles, for

example, protects the host from being infected again later. Thus, a person can contract

many disease s only once. Colds and inﬂuenza, on the other hand, stem from viruses

that continue to produce new strains that avoid the body’s predeveloped defenses, so

that they may be contracted repeatedly. Prior exposure also does not protect against

many microbial toxins, such as those involved in botulism food poisoning or against

some parasitic infections, such as schistosom iasis, tapeworm, and athlete’s foot.

Infection by a similar agent can in some cases provide protection from a disease.

Contracting cowpox, for example, protected people from later getting the much more

serious disease, smallpox. Similarly, it appears that having yaws (a disease caused by

the spirochete bacterium Treponema pertenue and spread by direct contact) offers protec-

tion from syphilis (caused by T. pallidum).

Acquiring immunity through vaccination has played a major role in the control of a

variety of diseases, particularly viral infections that are otherwise untreatable. This

involves exposing a person to a material that will stimulate immunity to a particular

agent. The mater ial used may be a killed, inactivated, or weakened strai n of the agent,

a portion of its surface, one of its products, or a closely related agent.

One of the greatest successes of vaccination has been with smallpox. This once devas-

tating disease killed millions in the Old World and scarred countless others. It was then

brought to the New World, where it killed milli ons of Native Americans, in some cases

wiping out entire cultures. In fact, the infection was spread intentionally to some tribes by

European invaders who distributed infected blankets (an early example of biological war-

fare). Vaccination with material from the pustules (pox) of victims was practiced in Asia

for at least several centuries, but sometimes lead to serious infection. In 1798, Edward

Jenner reported on his experiments and observations in England involving cowpox, a

related but mild disease of cows and milkmaids. He developed a vaccine based on this

virus that provided immunity to smallpox. Vaccination was so successful that by 1966,

the World Health Organization undertook a program to eradicate smallpox worldwide.

In part because humans are the only known reservoir, the aggressive surveillance (track-

ing) and vaccination programs succeeded—the last ‘‘natural’’ case of smallpox occurred

in 1977 (a small outbreak occur red among laboratory workers in England the following

year). Since the disease no longer exists (the virus has been stored in two laboratories, in

Atlanta and Moscow), vaccination has now been discontinued.

Another great success of vaccination has been with polio. This viral disease has now

been eliminated in the Americas, the western Paciﬁc, and Europe, and was scheduled for

worldwide eradication by the end of 2002. (This target was missed, with 12 countries in

Asia and Africa still not virus free as of early 2005; see www.who.org for updat es.)

Table 12.8 shows the vaccinations approved for use in the United States, with those

recommended for children and the general population indicated by footn ote a. Some,

such as DTP (diphtheria, tetanus, pertussis), are typically given as combined vaccinations,

although individual inoculations or other combinations are possible (marked as footnote

b). The others are designed for special populations that are at higher risk of a particular

CONTROL OF INFECTION 379

disease based on occupation (including the military), travel to areas where the disease is

endemic, or other factors. Most vaccinations are given as an injection, but a few are taken

orally.

In some cases, the immune system can be ‘‘helped’’ by injection of an immune globu-

lin, or antibody. Approved immune globulins are listed in Table 12.9.

TABLE 12.8 Licensed Vaccines and Toxoids Available in the United States

Vaccine Type Route of Administration

Adenovirus Live virus Oral

Anthrax Inactivated bacteria Subcutaneous

Bacillus of Calmette and

Guerin (BCG)

Live bacteria Intradermal/

percutaneous

Cholera Inactivated bacteria Subcutaneous or intradermal

Diphtheria–tetanus–acellular

pertussis (DTaP)

Toxoids and inactivated bacterial

components

Intramuscular

Diphtheria–tetanus–pertussis

(DTP)

Toxoids and inactivated whole

bacteria

Intramuscular

DTP–Haemophilus inﬂuenzae

type b conjugate (DTP-Hib)

Toxoids, inactivated whole bacteria,

and bacterial polysaccharide

conjugated to protein

Intramuscular

Haemophilus inﬂuenzae

type b conjugate (Hib)

Bacterial polysaccharide

conjugated to protein

Intramuscular

Hepatitis B

Inactive viral antigen Intramuscular

Inﬂuenza Inactivated virus or viral

components

Intramuscular

Japanese encephalitis Inactivated virus Subcutaneous

Measles

Live virus Subcutaneous

Measles–mumps–rubella

(MMR)

Live virus Subcutaneous

Meningococcal Bacterial polysaccharides of

serotypes A/C/Y/W-135

Subcutaneous

Mumps

Live virus Subcutaneous

Pertussis

Inactivated whole bacteria Intramuscular

Plague Inactivated bacteria Intramuscular

Pneumococcal Bacterial polysaccharides of 23

pneumococcal types

Intramuscular or

subcutaneous

Poliovirus vaccine,

inactivated (IPV)

Inactivated viruses of all three

serotypes

Subcutaneous

Poliovirus vaccine,

oral (OPV)

Live viruses of all three serotypes Oral

Rabies Inactivated virus Intramuscular or intradermal

Rubella (German measles)

Live virus Subcutaneous

Tetanus

Inactivated toxin (toxoid) Intramuscular

Tetanus–diphtheria

(Td or DT)

Inactivated toxins (toxoids) Intramuscular

Typhoid (parenteral)/

(Ty21a oral)

Inactivated bacteria/live bacteria Subcutaneous/oral

Varicella (chickenpox)

Live virus Subcutaneous

Yellow fever Live virus Subcutaneous

Part of standard recommended vaccination program for children.

Alternative form of recommended vaccination for children.

380 EFFECT OF MICROBES ON HUMAN HEALTH

12.8.3 Antibiotics and Antitoxins

Alexander Flemi ng in 1928 made a serendipitous discovery that Staphylococcus bacteria

would not grow in the presence of the fungus Penicillium notatum. Eventually, the active

ingredient, penicillin, was isolated and since 1941 it has been of great value in the control

of certain bacterial diseases, especially syphilis, pneumococcal pneumonia, and some

staphylococcal and streptococcal infections. Shortly thereafter, in 1943, Selman Waksman

and Albert Shatz found streptomycin, produced by the actinomycete Streptomyces gri-

seus, which was effective against tuberculosis and many gram-negative bacteria. In addi-

tion to many other antibacterials, compounds active against some fungi and protozoa have

since been developed, and most recently there has been success with antiviral compounds.

The term antibiotic dates from 1889, when Paul Vuillemin used it for a chemical com-

pound produced by Pseudomonas aeruginosa that was inhibitory to other bacteria.

An antibiotic is a chemical that can be used to control the activity of selected micro-

organisms, especially within the body (as opposed to a disinfectant, which is used outside

the body and which is not selective). Speciﬁc antibiotics are typically effective against a

particular range of pathogens. A wide array of antibiotics now exist, with many produced

by other organisms but some produced synthetically. Antibiotics have become a major

tool in the control of disease. However, strains of pathogens that are resistant to our pre-

sent antibiotics have emerged, and the search for new ones thus continues with a sense of

urgency.

In some case s it is a toxin produced by the microbial agent that is a major cause of

disease. Chemicals that are able to prevent or counteract these toxic effects are referred

TABLE 12.9 Immune Globulins and Antitoxins Available in the United States

Immunobiologic Indication(s)

Botulinum antitoxin Treatment of botulism

Cytomegalovirus immune

globulin, intravenous (CMV-IGIV)

Prophylaxis for bone marrow and kidney transplant

recipients

Diphtheria antitoxin Treatment of respiratory diphtheria

Immune globulin (IG) Hepatitis A pre- and postexposure prophylaxis; measles

postexposure prophylaxis

Immune globulin, intravenous (IGIV) Replacement therapy for antibody deﬁciency disorders;

immune thrombocytopenic purpura (ITP);

hypogammaglobulinemia in chronic lymphocytic

leukemia; Kawasaki disease

Hepatitis B immune globulin (HBIG) Hepatitis B postexposure prophylaxis

Rabies immune globulin (HRIG) Rabies postexposure management of persons not previously

immunized with rabies vaccine

Tetanus immune globulin (TIG) Tetanus treatment; postexposure prophylaxis of persons not

adequately immunized with tetanus toxoid

Vaccinia immune globulin (VIG) Treatment of eczema vaccinatum, vaccinia necrosum, and

ocular vaccinia

Varicella-zoster immune

globulin (VZIG)

Postexposure prophylaxis of susceptible

immunocompromized persons, certain susceptible

pregnant women, and perinatally exposed newborn

infants

CONTROL OF INFECTION 381

to as antitoxins. A few such compounds have been developed, including those effective

against botulism and diphtheria toxin (Table 12.9).

12.9 INDICATOR ORGANISMS

How do we know that the treated potable water entering the distribution system or coming

out of a residential tap is microbially safe to drink or bathe with? Has the disinfection of a

wastewater been effective? Is the water at the beach ‘‘swim mable’’? Can shellﬁsh be har-

vested from this bed?

Ideally, we might like to answer these questions by determining the concentration of

each speciﬁc pathogen and parasite in the water. However, this is clearly impractical for a

number of reasons, including the very large number of possible disease agents and the

resulting enormity of the job and treme ndous expense. Further, it is likely that not all

pathogens are known yet, and even for some of those that are recognized there is no

method to quantify them. Perhaps in the future, molecular techniques or other advances

may make this goal more nearly attainable, but for now it is necessary to rely on some

other approach.

12.9.1 Physical–Chemical Indicators

As a practical matter, there is a need for some real-time measures of the microbial qual-

ity of drinking water and the effectiveness of disinfection. Test s that take several days, or

in some cases even several hours, may be too slow to indicate that a problem has occurred

during treatme nt. By that time a drinking water may already have been consumed, or a

wastewater already discharged. The turbidity (cloudiness) of a water can serve as one

useful measure, since it can indicate failure of previous treatment steps, and since the

small particles imparting turbidit y might harbor pathogens. The chlorine residual

(concentration of active chlorine products remaining in the system) may also be of use

where chlo rination for disinfection is practiced. As another example, during autoclaving

(moist heat sterilization) of some laboratory and hospital supplies, tape impregnated with

a heat-sensitive chemical can be used to indicate that the appropriate temperature was

maintained.

12.9.2 Microbiological Indicators

Where real-time measures are not essential, or for use in conﬁrming their validity, it is

logical to consider monitoring of indicator organisms as surrogates for pathogens them-

selves. For example, certain bacteria present in feces might be used to indicate the pre-

sence of fecal pollution and hence the likelihood that pathogens are present. Other

organisms might be appropriate for other purposes, such as for evaluating swimming

pools.

Because a major public health conce rn traditionally has been contamination of drink-

ing, shellﬁsh harvesting, and recreational waters with sewage, considerable effort has

gone into developing methods for microbial indicators of feca l cont amination in such

waters. However, although several of these tests are used routinely and are generally

reliable, it is important to remember the purpose for which they were developed. These

382 EFFECT OF MICROBES ON HUMAN HEALTH

standard indicators may not be appropriate for all applica tions, especially those for which

they were not envisioned, such as microorganisms in aerosols.

Characteristics of an Ideal Indicator Organism The ideal microbial indicator of fecal

contamination would have a number of characteristics. (Note that similar characteristics

could be enumerated for other types of indicators as well.) First, it should be present in

human feces in high numbers, making the test sensitive and thereby avoiding false nega-

tive results (in which a test says that contamination is absent even though it is really pre-

sent). In fact, the ideal would be that the indicator to pathogen ratio would be high and

stable. However, it is recognized that a constant ratio, at least, is not feasible, since the

concentration of pathogens will vary based on the rate of infection in the population.

On the other hand, the indicator organism should be absent from uncontaminated mate-

rials (avoiding false positive results). In many cases, though, its presence in the feces of

other warm-blooded animals would be desirable, since som e diseases can be spread from

animal to humans, but this would depend on the particular application.

The indicator organism should also die off in the environment at a slightly slower rate

than the pathogens. Dying too quickly could lead to false negatives, while dying too

slowly would lead to false positive results.

In terms of the actual testing, it would be very nice if rapid, easy, and inexpensive

methods were available. Also, it would be preferable that the indicator organism itself

is not pathogenic. After all, we do not want a large number of labs growing up vast quan-

tities of potentially disease-causing organisms.

As might be expected, no ideal indicators are known. However, a number of methods

have been developed that meet the criteria above for indicators of fecal contamination or

other purposes to a useful extent. Several of these are described below. An important

source for the detailed procedures is Standard Methods for the Examination of Water

and Wastewater (Clesceri et al., 1998).

Total Coliforms Total coliforms are aerobic or facultatively anaerobic, gram-negative,

nonsporeforming rods that ferment lactose (milk sugar) with acid and gas production (gas

production not considered in an alternative procedure) within 48 hours (24 hours in the

alternative test) at 35



C. This is an operationally deﬁned group of microorganisms: that

is, organisms that show up as positive in the test are deﬁned as members of the group. The

test is designed to include selected members of the bacterial family Enterobacteriaceae,

especially many E. coli. This species is common (but not predominant) in the intestinal

tract of humans and other warm-blooded animals. Also, it is closely related to Salmonella

and Shigella, two of the bacteria historically of greatest concern for waterborne disease;

thus its die-away in the environment is likely to be similar. However, not all E. coli are

coliforms (e.g., some strains cannot ferment lactose), and not all coliforms are E. coli.

Examples of other members of the family Enterobacteriaceae that may include coliforms

are Enterobacter, Klebsiella pneumoniae, and Citrobacter. Additionally, some coliforms

can grow and survive in soil or water. Also, while they serve as reasonably good indicators

for Salmonella and Shigella, their survival of disinfection and various environmental

factors may differ substantially from that of some other disease agents, including other

bacteria, protozoa, and viruses.

Still, total coliforms are one of the most useful indicator groups for their intended pur-

pose. About 10

1

are commonly found in raw sewage. (In a practice dating from the

early years of the ﬁeld, microbial counts in water are often expressed ‘‘per 100 mL’’; the

INDICATOR ORGANISMS 383

same unit also is sometimes used for wastewater, so that this number of coliforms would

be 10

per 100 mL.) They are used rout inely to monitor the microbial safety of drinking

water supplies. Total coliform counts also may be helpful in evaluating the feca l contam-

ination of some foods and the disinf ection efﬁciency for wastewaters. Both an MPN and

an alternative membrane ﬁltration procedure are available (Section 11.5.2).

Fecal Coliforms Since not all coliforms are of fecal origin, it would be useful to have a

test that was more selective and included only fecal bacteria. The fecal coliform test

attempts to achieve this mainly by incubation at 4 4.5



C, hoping by the higher temperature

to eliminate bacteria that are better adapted to the lower soil and water temperatures of the

ambient environment. The test is partia lly successful in meeting its goals. It is estimated

that about 90% of the coliforms that grow at 44.5



C are of fecal origin (10% false

positives); however, only about 90% of the coliforms of feca l origin can grow at the

elevated temperature (10% false negatives). Additionally, precise control of the tempera-

ture is critical, as even 0.5



C higher can prevent the growth of many fecal coliforms, while

slightly lower temperatures allow the growth of more nonfecal organisms.

Fecal coliforms are considered good indicators for outdoor swimming pools and

recreational waters. (See also the fecal coliform/fecal strep ratio, below.) Again, both

MPN and membrane ﬁltration methods can be used.

Fecal Streptococci/Ent erococci Although also operationally deﬁned, the fecal strepto-

cocci consist mainly of Streptococcus faecalis, S. faecium, S. avium, S. bovis, S. equinus,

and S. gallinarum; the enterococci include only S. faecalis, S. faecium, S. aviu m, and

S. gallinarum. The ﬁrst two species tend to be more common in humans and rats, whereas

the others tend to be more common in chickens, cattle, horses, and dome stic fowl (birds),

respectively. However, they are not truly host-species speci ﬁc.

The fecal streptococci are common inhabitants of the intestinal tracts of warm-blooded

animals. In fact, humans are atypical in that they usually have a greater number of coli-

forms than fecal streptococci; in most other species, the fecal streptococci are more

numerous. Thus, for fresh contamination (the ratio changes with age), a fecal coliform/

fecal streptococci ratio of 4 may be considered indicative of human pollution, whereas a

ratio 0.7 suggests an animal source.

The enterococci are now usually considered the best indicator for recreational surface

waters, particularly ocean beaches. Once again, both MPN and membrane ﬁltration meth-

ods are available. Incubation is at 35



C for 24 to 48 hours, depending on the test used.

Heterotrophic Plate Count The heterotrophic plate count (HPC), sometimes called

the standard or total plate count, uses a nonselective medium in an attempt to include

as many of the bacteria present as possible. Incubation is at 35



C for 48 hours or at 20

to 28



C for 5 to 7 days. One use of the HPC is that increases can indicate problems in

water treatment processes or potable water distribution systems. High counts in indoor

pools indicate poor disinfection and/or overuse or inadequate cleaning. Available tests

include pour plate, spread plate, and membrane ﬁltration methods.

Speciﬁc Organisms In some cases, tests for speciﬁc organisms may be desirable. For

example, in indoor swimming pools and whirlpools or spas, tests for Pseudomonas aer-

uginosa and Staphylococcus are recommended. These organisms serve not only as indi-

cators of microbial loadings from skin and mucous membranes, but are themselves

384 EFFECT OF MICROBES ON HUMAN HEALTH

pathogens of potential concern. (HPC serves as a recommended indicator of disinfection

efﬁciency for these systems.) Clostridium perfringens, which as an endosporeformer can

persist for long periods in the environment, has been used to monitor the dispersal of was-

tewater treatment sludges disposed of in the ocean (now banned in the United States).

Some coliphage (viruses that infect E. coli) have been used to monitor disinfection.

Coliphage F2 has been found to be very heat resistant and was thus used as a conservative

indicator (one that provides an extra margin of safety) during the development of criteria

for pathogen destruction during composting. In monitoring microbial aerosols generated

during composting operations, Aspergillus fumigatus has sometimes been used, since its

spores will survive longer than coliforms, and since it is itself of concern.

These examples are meant to be illustrative rather than exhaustive. Remember, the

available indicators were developed for certain purposes and should not be adopted arbi-

trarily for other situations.

PROBLEMS

12.1. Bulking is a ‘‘disease’’ of activated sludge wastewater treatment plants (see Section

16.1.3) in which the excessive growth of ﬁlamentous organisms interferes with

normal settling. Escherichia coli is commonly found at high concentrations (e.g.,

1

) in activated sludge, and sometimes grows in short chains when grown in

the laboratory on agar medium. This led some early investigators to suggest

erroneously that E. coli was the cause of bulking. How might knowledge of Koch’s

principles have helped these researchers avoid this error?

12.2. The hot-water system at a motel contains 3:0  10

1

viable cells of Legionella

pneumophila. A guest takes an 8-minute shower with the water running at 2.5 gal/

min, 60% of it hot water. Assuming that 0.1% of the cells present are aerosolized

and that 1% of those are inhaled, is this person likely to develop Legionnaires’

disease if the infective dose is 100,000 cells? (Note: The actual infective dose for

Legionnaires’ disease is not known.)

12.3. With regard to the fecal–oral route of water borne disease, what steps can be taken

to break the chain of infection?

12.4. What factors make total coliforms a good indicator for monitoring of drinking

water? What are some of the group’s limitations as an indicator for this purpose?

12.5. What are some of the points that should be considered in selecting indicator

organism groups to be used for monitoring a public swimming pool?

REFERENCES

Atlas, R. M., and L. C. Parks (Eds.), 1997. Handbook of Microbiological Media, 2nd ed., CRC Press,

Boca Raton, FL.

Centers for Disease Control and Prevention. www.cdc.gov.

Clesceri, L. S., A. E. Greenberg, and A. D. Eaton (Eds.), 1998. Standard Methods for the Examination

of Water and Wastewater, 20th ed., American Public Health Association, Washington, DC.

Updated regularly and available at www.wef.org.

REFERENCES 385

Murray, P. R . (Ed.-in-Chief), 1999. Manual of Clinical Microbiology, ASM Press, Washington, DC.

Scheld, W. M., W. A. Craig, and J. M. Hughes (Eds.), 2001. Emerging Infections, Vol. 5. ASM Press,

Washington, DC. See also Vols. 1 to 4.

World Health Organization. www.who.org.

386

EFFECT OF MICROBES ON HUMAN HEALTH

MICROBIAL TRANSFORMATIONS

In this chapter we focus on the role that microorganisms play in the cycling of elements

important to life. Unlike the organisms themselves, these atoms never ‘‘die’’ or dis-

appear. Instead, they continuously pass through a grand set of biogeochemical cycles

whose mechanisms, although carried out at times on a minute scale, are vital to life.

Quantitative aspects of these cycles, and their interactions with other parts of ecosystems,

are described in Chapter 14.

These biogeochemical cycles include a variety of metabolic pathways as well

as abiotic reactions that continuously replenish the chemical ingredients of life.

Microbes are the agents of most of these reactions, often through adding electrons

to and removing electrons from atoms within a sequence of redox reactions. Often,

it is only microbes that can carry out a speciﬁc reaction. In some other cases, the

reactions might still occur without microorganisms, but only at much lower rates.

Atoms found in living organisms, whether macro, micro, or trace ingredients,

were at one time in inorganic, nonliving materials and eventually will be released

from their assimilated organic forms and returned to an inorganic state. Thus, the

microbial reactions not only create essential materials (e.g., reduced nitrogen com-

pounds) but also eliminate unwanted, and potentially harm ful, residuals (e.g., waste

and decay products generated through the normal course of life and death).

In a few cases, essential elements occur almost entirely in one oxidation state.

Phosphorus, which occurs almost solely (exceptions include some pesticides and nerve

gases) in the form of phosphate, is a prime example. These elements are still potentially

cycled between organic and inorganic forms, but through hydrolysis or other such reac-

tions, not through oxidation or reduction.

Environmental Biology for Engineers and Scientists, by David A. Vaccari, Peter F. Strom, and James E. Alleman

387