Bacteriology for students in general and household science

Front matter

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Preface To The Second Edition

CHANGES in point of view and development in the science of bacteriology have made necessary a revision of the text. Several chapters have been completely rewritten. The work of the Committee on Nomenclature of the Society of American Bacteriologists has made advisable the revision of the scheme of classification and of names of bacteria. The chapter on the effect of physical agencies on microdrganisms has been extended by consideration of these effects upon the life phases of a culture. Several other chapters on physiology have been extensively revised. Marked advance in our knowledge of the scientific basis of food preservation requires elaboration of this topic. Increased emphasis has also been put upon panary and lactic acid fermentations. Most of the remaining chapters have required some modification.

It has also seemed advisable in preparing this second edition to increase the scope of the text to meet the needs of students in non-technical courses, that is, those enrolled in curricula in general science and liberal arts as well as those interested primarily in household science.

R. E. BUCHANAN.

Ames, Iowa, October, 1921.

Preface To The First Edition

Tuis volume is a revision of the lectures given during the past eight years to students in Home Economics at the Iowa State College of Agriculture and Mechanic Arts.

Several texts have appeared in recent years which include a part at least of the subject matter of bacteriology in its relationships to domestic science, but so far as the authors are aware there is no single text devoted wholly to this topic. Much of the material here given is fundamental to a proper consideration of many of the other courses usually prescribed for students of domestic science ; indeed bacteriology is quite generally among the required subjects for students of this subject. It is hoped that this volume may prove helpful to those who are teaching this work.

It will be noted that bacteriology is herein defined to include a consideration of the true bacteria, the yeasts, the molds, and the pathogenic protozoa. An attempt is made to discuss the morphology and classification of the yeasts and molds more fully than is customary in most texts. The illustrated key in the appendix has been of considerable assistance in our own laboratories. This key is by no means exhaustive; but very rarely indeed have our students encountered forms that could not be identified satisfactorily by its help.

The volume has been divided somewhat arbitrarily into five sections. The first on morphology and classification, the second on cultivation and observation of microdrganisms, and the third on physiology, are in a sense introductory. The fourth section on fermentations and the fifth on the relationships of microorganisms to health are planned to point out anc emphasize the relationships of bacteriology to the preparation and preservation of foods, and to household sanitation and personal

ix x PREFACE hygiene. It is in no sense, however, intended as a text on sanitation or hygiene.

The assistance of Miss Anna Wolfe and of Dr. Charles Murray in the preparation of manuscript and the reading of proof is gratefully acknowledged. ; E. D. BUCHANAN,

R. E. BUCHANAN.

Ames, Iowa, August 12, 1912.

Contents

CHAPTER PAGE

15; DAPRODUCTION 4). 2, « ayecd Hour etinin Se thas « Ane eos oe aromas

Historical Theory of Spontaneous Generation—Germ

Section I Morphology, Classification, And Distribution Of Microorganisms

II. Posrrion oF MIcROORGANISMS IN THE PLANT AND ANIMAL RUMGDOME $5 inh. Stara eee ee ete eee Organisms included in Bacteriology—Differences between Plants and Animals—Divisions of the Plant Kingdom— Differentiation of Bacteria, Yeasts, and Molds—Groups of

the Animal Kingdom.

Ti, Monpuosoot ov tam Bactmeta.. «53s: seen ches ss ten Shape of Bacterial Cells—Arrangement and Grouping of Bacterial Cells—Size and Measurement of Bacteria—Struc-

ture of the Bacteria—Reproduction of Bacteria.

Use of Generic and Specific Names—Difficulties in Bac-

terial Nomenclature—Systems of Classification of Bacteria— Discussion of Important Genera,

Vi: Momrnerecy OF THE-VmAstS ooo. seuss 3 0, onan ene Shape and Grouping of Cells—Size—Structure—Reproduction—Spore Produ¢tion.

VL. Cramimrigation on Tam YRAsts. eros | eh dh es True and False Yeasts—Relationships of the Yeasts— Classification of True Yeasts—Important Genera.

Vil. Mandmotoor oF 7am RECUR. 1. aS Tae Plant Body—Structure of the Mycelium—Growth— Reproduction.

xl xii

CHAPTER

VIII.

XII.

XIII.

XIV.

XV.

CONTENTS

CCAMMISECATOON OF THE BEOLDS. .. 2.0... 62 ck cece eee es

Limitation of the Term Mold—Botanical Relationship

of the Molds—Classification of Molds—Key to the Impor-

tant Families and Genera of Molds—Important Genera and Species of Molds.

DISTRIBUTION OF MICROORGANISMS. ...........-0eseeeees Microérganisms of the Soil—Microérganisms in Water —Microérganisms in Foods—Microérganisms in Fermentation and Decay—Microérganisms of the Body—How Microérganisms are Scattered.

Section II Cultivation And Observation Of Micro- Organisms

EES Pete PEE Oe Or PE ae Pe Sterilization by Heat—By Filtration—By Light.

UsES AND PREPARATION OF CULTURE MEDIA............... Characters of the Nutrient Medium—Non-synthetic Media—Synthetic Media.

Poem CORPOnO DIMUEIODE. 6.2... 5 oes s ges ye and sand be

Pure and Mixed Cultures—Methods of Transfer—

Methods of Securing Pure Cultures—Chart of American Society of Bacteriologists.

Stupy oF GROWTH CHARACTERS IN PURE CULTURES........ Cultural Characteristics of Bacteria—Cultural Characteristics of Yeasts—Cultural Characteristics of Molds.

STUDY OF PHYSIOLOGICAL CHARACTERS, ...1......s.05s005 Acid Production—Alcohol Production—Reduction of Nitrates to Nitrites—Reduction of Sulphates—Reduction of Pigments—Production of Ammonia—Production of Indol—Digestion of Starch—Of Gelatin—Of Blood Serum— Of Casein.

METHODs OF MICROSCOPIC EXAMINATION. .........0-0-0005 Optics of the Oil Immersion Lens—Preparation of Non-permanent Mounts—Preparation of Stained Mounts.

PAGE i ee a

— i a retin ial

CHAPTER

XVI.

XVII.

XVIII.

XIX.

XX.

XXII,

CONTENTS xiii

Section III Physiology Of Microorganisms

EFFECTS OF PHysICAL AGENCIES ON MICROORGANISMS... .. 159 Moisture and Osmotic Pressure—Light—Temperature.

RELATIONSHIP OF MICROORGANISMS TO CHEMICAL ENVI- OUI. «eo -ttinst shh pl names bane ae 173 Free Oxygen—Efiect of Chemicals on Movement— Effect of Chemicals on Growth—Inhibition of Growth and Destruction of Microérganisms by Chemicals—Antiseptics and Disinfectants—Symbiosis—Antibiosis—Metabiosis—Commensalism.

PHYSICAL EFFECTS PRODUCED BY MICROORGANISMS ........ 190 Heat Production—Light Production—Changes in Consistence—Changes in Osmotic Pressure.

CHEMICAL SYNTHESES BROUGHT ABOUT BY MICROORGAN-

Réle of Food in Organisms—Differentiation of Products of Synthetic and Analytic Action—Anabolism— Katabolism—Metabolism—Groups of Synthetic Products.

ANALYTIC CHANGES BROUGHT ABOUT BY MICROORGANISMS... 201

General Discussion—Cycles of the Elements in Nature and Parts played by Microérganisms—Nitrogen Cycle— Carbon Cycle—Sulphur Cycle—Phosphorus Cycle.

Section IV Fermentation Or Zymotechnique General Discussion Of Fermentation... ..........0.0005 209

XXII. Enzymes or MICROORGANISMS AND THEIR ACTIVITIES....... 214

Origin of Enzymes—Characteristics of Enzymes— Intracellular and Extracellular Enzymes—Groups of Enzymes—Autolytic Enzymes.

xiv CONTENTS

CHAPTER XXIII. MicroOrGANisMsS AND Foop PRESERVATION............. Need of Food Preservation—Agencies tending to change Food Materials—Methods of Food Preservation—Heat—Cold—Preservative Substances— Drying.

XXIV. CHANGES PRODUCED BY MICROORGANISMS IN INORGANIC

Sl ucs doi 3) 1, iil emma Se cee Set oS a ea

Nitrogen—Fixation—Oxidation— Reduction — Sulphur—Oxidation—Reduction—Phosphorus—Carbon.

XXV. CHANGES PRODUCED BY MICROORGANISMS IN Non- NITROGENOUS ORGANIC SUBSTANCES. ALCOHOLIC PSO AINI s k k e ce Wdvipian's vices v's os

Types of Organisms—Yeasts—Molds—Bacteria— Enzymes—Alcoholic Fermentation of Fruit Juices— Alcoholic Fermentation in Brewing—Alcoholic Fermentation of Milk—Fermentation for Distilled Liquors and Commercial Alcohol—Panary Fermentation.

XXVI. CHANGES PRODUCED BY MICROORGANISMS IN NON- NITROGENOUS ORGANIC SUBSTANCES (Continued). Lacric Act FERMENTPATION...................-.

Materials which commonly undergo Lactic Acid Fermentation—Lactic Acid Fermentation of Milk—Composition of the Milk—Sugar Content—Origin of Lactic Organisms in Milk—Groups of Lactic Organisms— Bacillus lactis acidi and Streptococcus lacticus Group —Bacillus coli and Bacterium lactis aerogenes Group —Bacillus bulgaricus Group—Proteolytic Acid Bacteria—Lactic Acid Fermentation of Sauerkraut—Lactic Acid Fermentation of Other Food Materials.

XXVII. CHEMICAL CHANGES BROUGHT ABOUT IN NON-NITROG- ENOUS ORGANIC MatTer (Continued). ACETIC, Burvnic, Crreic, anp OxAere ACips.)¢... 5. ..... Acetic Acid Production—Butyric Acid Fermentation—Citric Acid Fermentation—Oxalic Acid Fermentation—Other Acid Fermentations—Oxidation of

Organic Acids by Molds.

a a ee

_

CONTENTS

CHAPTER

XXVIII. CHANGES PRODUCED BY MICROORGANISMS IN NOn- NITROGENOUS ORGANIC SUBSTANCES (Continued). TRANSFORMATION OF POLYSACCHARIDES, HIGHER ALCOHOLS,» FAW yj MIC 3 sutret ty 28 tere RR a athe Fermentation of Cellulose—Fermentation of Starch, etc——Fermentation of Hemicelluloses—Fermentation of Pectin—Fermentation of Gums—lInversion of Disaccharides—Fermentation of Fats—Fermentation of

Fatty Acids—Fermentation of Paraffins.

XXIX. CHANGES PRODUCED BY ORGANISMS IN ORGANIC NITROGE- Nous COMPOUNDS. GENERAL DISCUSSION......... Structure of the Protein Molecule—Steps in Disintegration of the Protein Molecule—Proteins to Proteoses and Peptones—Peptones to Amino Acids, etc.— Amino Acids to Ammonia—Formation of Flavoring Substances—Formation of Substances having Disagreeable Odors—Formation of Ptomaines.

XXX. CHANGES PRODUCED BY ORGANISMS IN ORGANIC NITROGE- Nous CompounDs. MEATS AND CHEESE.......... Ripening of Meats—Ripening of Cheese—Sour Curd Cheese—Hard Rennet Cheeses—Soft Rennet Cheeses.

Section V Microorganisms And Health

XXXI. GENERAL DISCUSSION OF DISEASE............ Sows Theories of Disease—Spread of Disease—Classification of Diseases—Uses of Animals and Animal In-

oculation in the Bacteriological Laboratory.

XXXII. RESISTANCE OF THE Bopy TO DISEASE................+% Immunity—Natural Body Barriers to Infection—

Factors predisposing to Disease—Types of Immunity

—Theories of Immunity—Use of Terms Antigen and Antibody—Antitoxins and Related Antibodies—Toxins—Antitoxin—Theories of Structure and Origin of

Toxin and Antitoxin—Agglutination and Precipitation -

—Cytolysins—Opsonins—Anaphalaxis and Hypersusceptibility—Vaccines, xvi

CHAPTER

XXXITI.

XXXIV.

XXXV.

XXXVI.

XXXVIT.

XXXVIII.

AXXIX.

XLIi.

CONTENTS

MIcROORGANISMS NORMAL TO THE HUMAN Bopvy.......

Flora of the Skin—Of the Mouth—Of the Stom-

ach and Intestines—Of the Respiratory Tract—Of the Genito-urinary System.

CLASSIFICATION OF DISEASE-PRODUCING ORGANISMS

Pathological Classification—Bacteriological Classification—Groups—Bacteria producing Disease— Yeasts producing Disease—Molds producing Dis-. ease—Protozoa producing Disease—Ultra-microscopic Viruses and Diseases of Unknown Cause.

Group or NON-SPECIFIC PYOGENIC COCCI............. Micrococcus aureus—Micrococcus albus—Streptococcus pyogenes—Streptococcus lacticus.

PEACOM CHROOP ak es SNES odes ones ch Pasteurella pestis.

CRP SR OED CPR ae es cess cedaes Colon Group—Bacillus coli—Intermediate Subgroup—Bacillus paratyphosus—Bacillus enteriditis— Typhoid Subgroup—Bacillus typhosus—Bacillus dysenteri@.

Acip-FasT oR TUBERCULOSIS GROUP.............0005 Bacillus tuberculosis—Bacillus lepre.

PATHOGENIC SPORE-PRODUCING ORGANISMS...........- Bacterium anthracis—Bacillus tetani—Bacillus botulinus.

ay LOPS ETL R STEEL COE Ce Vibrio cholere—Non-pathogenic spirilla.

CONTENTS XVii

CHAPTER PAGE BLAM. PArHocenw YHAsts AND MOLDS. ..6. 4.0. sot sig hao oure 448 Blastomyces—Aspergillus—Microsporon—Oidium.

LIV .. Patnocminc PROMZOA.: |). :: 2:).. 45-225 400 agen eae ee 452 Amceba and Entamceba—Spirocheta and Treponema—Trypanosoma—Plasmodium.

XLV. DISEASES WHOSE CAUSES ARE UNKNOWN................ 405 Smallpox—Chicken Pox—Yellow Fever—Typhus Fever—Rocky Mountain Spotted Fever—Epidemic Infantile Paralysis—Hydrophobia.

XLVI. Water CONTAMINATION, EXAMINATION, AND PURIFI- Cs 05. 55 bo rks ee Re ee 472 Flora of Pure Water—Flora of Impure Water—Relationship of Water to Health—Bacterial Examination of Water—Quantitative Methods—Qualitative Methods— Purification of Water.

XLVII. Arr CONTAMINATION AND EXAMINATION................. 488 Microérganisms commonly found in the Air—Numbers of Microédrganisms in the Air—Relationship between Dust and Bacteria.

XLVIII. Mix, rts CONTAMINATION AND EXAMINATION........... 404 Germicidal Action of Milk—Souring of Milk—How Bacteria gain Entrance to Milk—Factors determining the Numbers of Bacteria in Milk—Transmission of Disease by Milk—Methods of Milk Analysis—Classification of Milk.

XLIX. Foop (@xcepTinc MiILxk), rrs CONTAMINATION BY IN- JURIOUS MICROORGANISMS AND ITS EXAMINATION 506

Appendix

Ky TO THE FAMILIES AND GENERA OF THE COMMONER MOLDS........ 511 et a WO oo sok ns 67s sends Pa pe eg ee eee 549 ND 5 7 4.0k co oe ya ¥ te Le head 60 eaaletee wee 550

Chapter I Introductory And Historical

BACTERIOLOGY may be defined as that branch of science which treats of the forms, functions, and activities of bacteria. The lines of demarcation between the bacteria and the yeasts and molds on the one hand, and certain of the protozoa on the other, are very poorly marked. Furthermore, these latter groups are studied most readily by the methods that have been developed in the bacteriological laboratory. The meaning of the term Bacteriology has, therefore, gradually broadened until now it is generally understood to include a consideration of the true bacteria, the yeasts, the molds, and certain of the protozoa. The word Microbiology is sometimes used in the same sense and possibly may supplant Bacteriology as a more general and appropriate term.

Bacteriology has developed so rapidly that several subdivisions are now recognized. The morphology, physiology, classification, and cultivation of microdrganisms may be grouped under the heading of General bacteriology. A knowledge of these fundamentals is prerequisite to a study of applied bacteriology. Fermentations or zymotechnique is that branch of bacteriology in which especial attention is paid to chemical changes produced by bacteria, yeasts, and molds. These changes are often brought about in foods and may be useful or harmful in their preparation and preservation. Medical or pathogenic bacteriology treats of the bacteria that cause B I disease in man and animals. A knowledge of the most important characteristics of some of these organisms is self-evidently desirable for those who have care of the sick. So, too, is a knowledge of immunity or the means used by the body in the elimination and prevention of disease. Sanitary bacteriology includes a consideration of the manner in which disease-producing organisms are disseminated and of the methods used in preventing their distribution. Dairy bacteriology describes the organisms present in milk and other dairy products. A discussion of bacteriology, then, from the standpoint of general and household science should include a consideration of the fundamentals of the science, and of those portions of zymotechnique, medical, sanitary. and dairy bacteriology that have a bearing on preparation and preservation of food, and the conservation of health.

HISTORICAL

Bacteriology as a science is comparatively new, practically all of the work having been accomplished since 1860, and by far the greater portion since 1890. Four distinct factors are to be considered in an historical review of the subject: first, the history of the microscope, for its perfection necessarily antedated the development of this science; second, the theory of spontaneous generation; third, the germ theory of fermentation and decay ; and fourth, the germ theory of disease.

History of the Microscope and the Discovery of Bacteria.— Conjectures as to the existence of living beings smaller than are visible to the naked eye were made by the philosophers and physicians of ancient Greece, but it was not until the seventeenth century that microscopes were sufficiently perfected to allow such organisms to be seen.

The first record of observation of bacteria is that made by Leeuwenhoek, a Dutch lens maker, in 1683. He constructed and used a lens sufficiently powerful to enable him to see bacteria in the tartar from teeth and in various decaying organic substances. His drawings are sufficiently accurate to enable us

HISTORICAL 3 to recognize and identify with a considerable degree of certainty the organisms that he saw.

Improvement of the compound microscope had ‘so far advanced about one hundred years later (1786) that Miiller was enabled to formulate the first classification of bacteria. He introduced some of the terms that we still use, such as bacillus, vibrio, and spirillum. He did not, however, differentiate between bacteria and protozoa. Better lenses and improved microscopes enabled Ehrenberg in 1836 to work out a logical classification of the groups of bacteria. Dolland in 1844 first used the principle of immersion with the lens. This later evolved into the oil immersion objective of the modern microscope. The substage condenser of Abbé, developed in 1870, enabled the lens maker to. perfect higher power objectives. Every increase in definition and magnification added to the value and reliability of the work done with the microscope, and every such advance was marked by better knowledge of the morphology of the bacteria.

There has been comparatively little increase within recent years in the magnification of the microscope, due to a combination of two factors. First, higher magnifications necessitate more convex and smaller lenses with consequent increase in the difficulty of grinding and adjusting. Second, one of the optical laws developed by the physicist is to the effect that a clear view and determination of size and shape cannot be secured when the object which is examined is smaller than one half the wave length of the rays of light used for its examination. It is not probable that the magnification of the best lenses in use at present can be greatly increased.

Theory of Spontaneous Generation. — In ancient times and during the Middle Ages it was commonly believed that many forms of life could originate de novo. Frogs and worms were supposed to spring from the mud of ponds and streams, vermin of all kinds from decaying organic matter. Not until 1668 was this idea seriously questioned. Redi then showed that maggots would not inevitably develop in meat allowed to decay. He hit upon the simple expedient of tying a screen over the mouth of a jar to prevent the entrance of flies, and proved by his observations that maggots developed only from the eggs of the fly and could never form spontaneously. Other investigators soon showed the same facts to be true of other vermin. The theory was therefore abandoned with reference to the higher animals, but not with respect to microorganisms.

The observation that decaying organic matter always swarmed with bacteria led to the natural assumption that they were formed de novo as a product of the dead cells. Supposed proof of such development was furnished by boiling a decoction of some meat or vegetable, whereupon it was frequently found that organisms developed. It was assumed that boiling was sufficient to kill all organisms, and that their development in the boiled fluid proved the contention of those who believed in spontaneous generation. We know now that some common species of bacteria may not be destroyed at this temperature, and that these conclusions were not wholly correct. Spallanzani (1777) noted that organisms usually would not develop in organic materials that had been boiled for a time and hermetically sealed. His results were criticized for the reason that air was excluded from his flasks, and it was contended that the presence of air was essential to spontaneous generation. Schulze in 1836 passed air through sulphuric acid into flasks partially filled with boiled decoctions. He found that such air did not induce the development of the organisms. Schwann in 1837 demonstrated the same fact by passing the air through hot tubes. Even these demonstrations did not entirely disarm those who upheld the theory of spontaneous generation. They contended that air passed in this way through sulphuric acid or hot tubes was devitalized. They believed that air was an essential to spontaneous generation through its stimulating action on the organic matter with which it came in contact; the opponents of the

HISTORICAL § theory contended that the air itself contained the microérganisms in suspension, and when opportunity arose, they seeded the flasks. These experiments, therefore, did not satisfactorily settle all the points of contention.

Three series of experiments about the middle of the nineteenth century finally answered all objections and proved that life must come from preéxisting life of the same type, and that there is no spontaneous generation. Schréder and Dusch in 1854 showed that the filtration of air through sterile cotton removed its power of inducing the development of organisms in boiled liquids. It is scarcely conceivable that the cotton should act in any other way than as a filter. The assumption was, of course, that it removed all living particles from the air. This demonstration of the efficiency of the cotton filter is the basis for the universal practice in the bacteriological laboratory of sealing sterile materials in test tubes and flasks by means of cotton plugs. Pasteur in 1860 showed that communication might be maintained between the flask and the open air through a long tube so bent as to minimize the chance of any particles floating in the air gaining entrance and seeding the liquid. Finally Tyndall definitely proved the causal relationship of the floating matter of the air to the development of organisms. He first sought for a test whereby the complete absence of floating matter in the air might be ascertained. He found that a beam of light passed through an opening in a box was visible as it passed through the interior if any particles were floating in the air. When the air in such a box had been completely freed of floating matter by sedimentation, it was found that this air no longer would induce the development of organisms in boiled solutions. The cumulative effect of these three lines of evidence has been to establish certainly the falsity of the doctrine of spontaneous generation, and to justify the conclusion that living organisms of all kinds must originate from preéxisting organisms of the same kind. The whole matter is now one of historic importance only.

Germ Theory of Fermentation and Decay. — After the discovery of microdrganisms in many fermenting and decaying materials, the question naturally arose, Are these organisms responsible for the changes going on or are they simply attracted or possibly nourished by chemical changes proceeding independently of them? Do the bacteria produce the changes or do the changes simply make conditions right for the bacteria?

The thesis that the organisms are incidental and not causal was upheld with great vigor by the great German chemist, Liebig. He dominated the field of chemistry from 1840 to 1860, and few had the temerity to question his conclusions. Pasteur, however, from time to time published experimental results, from which he concluded that microérganisms are the primary cause of fermentations. These conclusions were strenuously opposed by Liebig, who ridiculed them as puerile and unworthy of serious consideration. Pasteur continued to pile up evidence such that at last Liebig was silenced. He succeeded in showing among other things that alcoholic fermentation is due to yeasts, and the souring of milk to bacteria. Since that time the evidence has grown until now we know that putrefaction, fermentation, and decay in general are due to the growth of microérganisms, and in most cases the particular forms ‘responsible have been isolated and studied. These facts aided also in the development of the germ theory of disease, and have given us much important and valuable information concerning the transformation of various organic compounds in nature, the purification of water, the disposal of waste, the enrichment of soils, and the changes that occur in foods.

The Germ Theory of Disease. — Plenciz (1762) first clearly stated the theory of the relationship of microédrganisms to disease. He claiméd that each disease was caused by a particular kind of organism, and that these organisms could be carried from one person to another by the air. He did not develop any experimental proof of his theories, however; they were wholly speculative. The first satisfactory demonstration

HISTORICAL 7 of the causal relationship of organisms to disease was secured by Davaine in 1863, when he showed that anthrax in animals is due to a specific bacterium and that the disease may be transmitted by a transfer of the organisms to a healthy individual. This relationship was worked out even more satisfactorily by Pasteur in 1865 when he proved the cause of an exceedingly destructive silkworm disease to be a protozoan parasite. Methods of growing organisms in the laboratory enabled Pasteur, Koch, and others to make still more satisfactory determination of their relationships to disease. In 1882 Koch introduced liquefiable solid’ media. This greatly simplified the securing of pure cultures. from mixed cultures, and their use was soon followed by the isolation and identification of the organisms causing a considerable number of diseases. To this discovery and the application of staining methods originated by Weigert, we owe the rapid advance that occurred during the last two decades of the nineteenth century in knowledge of the cause of disease. ‘To-day we know the causes of most of the infectious diseases of man and animals, although a few still baffle the investigator.

The development of the germ theory of disease has determined largely the direction and magnitude of growth of modern sanitary science and preventive medicine. Murchison’s pythogenic theory also had considerable ‘influence, particularly in England and the United States. According to this theory, disease is caused by the emanations arising from decaying or putrefying matter, and by the consumption of such materials in food and in water. Although finally superseded by the germ theory of disease, it rendered a real service in helping to bring about the formulation and adoption of practicable methods for the disposal of sewage and refuse, of an adequate system of plumbing, and of methods of water purification.

ih

; al 7 fe nae e Cer. i _

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Section I Morphology, Classification, And Distribu- Tion Of Microorganisms

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Ce Lal es | it OS ; ‘ a 1 Ss ’ : . 4 % ee ee Oe, Oe My ay oO aoe a a

Chapter II Position Of Microorganisms In The Plant And Animal Kingdoms

Organisms included in a Discussion of Bacteriology. — There is no single satisfactory English word that includes all of the forms of life comprised within the scope of bacteriology. We have already noted that there are four distinct groups to be considered: the bacteria, the yeasts, the molds, and the protozoa. To include all these the French word microbe and the English microérganism are perhaps the most satisfactory. Sometimes the term germ is similarly used, but this has so many meanings that its retention in this sense is not advisable.

It should be noted that the first three of the groups enumerated above, the bacteria, yeasts, and molds, belong to the plant kingdom, while the protozoa belong to the animal kingdom.

Differentiation of Plants and Animals. —It is not difficult to differentiate between the higher animals and the higher plants, since there are many points of contrast plainly to be seen. With the microscopic organisms much greater difficulty is often experienced; in fact, some intermediate forms are known that constitute a complete series of intergradations between the two groups. This difficulty is most pronounced between the bacteria and the protozoa, the simplest representatives of the plant and animal kingdoms respectively. In general it may be stated that the plant cell differs from that of the animal by the possession of a firm and well-differentiated wall, wholly distinct from the contained protoplasm. The bounding surface of the animal cell is more often simply an outer portion of the protoplasm, and impossible of separation from it. This distinction

at breaks down with some protozoa when they secrete a firm membrane and go into a resting state, or encyst. The line of demarcation is perhaps faintest between certain spiral bacteria and spiral protozoa. In this instance a means of differentiation has been found in the manner of multiplication; the bacterial spirals multiply by dividing transversely, the protozoan by longitudinal division. The statement is sometimes made that bacteria resemble animals more than plants in the composition of the cell wall. The typical cell wall of plants is made up of od) 4

Fic. 1. Intergradations between bacteria and protozoa. A, Spirillum. B, Microspira. C, Spirosoma. JD, Spirochete. E, Treponema. A, B, and C are bacteria; D and E are protozoa. (D adapted from Gonder, remainder original.)

cellulose, or one of its derivatives ; the limiting membrane of the animal cell is nitrogenous and, in those cases where a heavy cell wall is formed, chitinous. The cell walls of some bacteria have been shown likewise to be chitinous. The argument that this indicates the animal nature of the bacterial cells is vitiated by the fact that many of the molds, which all agree are plants, are known to have chitinlike cell walls.

The bacteria intergrade also with that group known as the “blue-green alge’? or Schizophycee. These forms possess chlorophyll and are obviously plants. Structurally many of them are practically identical with bacteria, and this constitutes a very strong argument for the plant affinities of the latter.

POSITION OF MICROORGANISMS 13

Many bacteria are motile, swimming about actively in water by means of flagella. This should not be regarded as an exclusively animal characteristic, for many plant cells are known to be motile; the sperm cells of mosses and ferns, for example, have flagella.

Divisions of the Plant Kingdom. — Plants are divided into four great groups: the Spermatophyta or seed plants, the Pterido-

Fic. 2. To illustrate the fact that organs of motion and motility are not exclusive animal characteristics. A, Euglena, a unicellular green alga. B, motile sperm of the Chara, one of the alge. C, motile sperm of a moss. D, motile sperm of a fern. £, motile bacterial cells. F, a motile protozoan from stagnant water. G, a trypanosome. H, Treponema, A, B, C, D, and E, are plants or plant cells; F, G, and H are protozoan cells. All of these cells are motile by means of flagella or cilia.

phyta or fern plants, the Bryophyta or moss plants, and the Thallophyta or thallus plants. The last group is the one that includes the bacteria, yeasts, and molds. It is differentiated from all other groups of plants by the lack of a complex plant body. Sometimes the plant consists of but a single cell, frequently of a thread of cells united end to end, but never forming a complex plant tissue with differentiation into roots, stems, and leaves.

The group Thallophyta is a very large one, containing tens of thousands of species. It is usually divided into three subgroups:

the Schizophyta or fission plants, the Alge, and the Fungi. The members of the group Schizophyta are distinguished from all other plants by being unicellular, and by having no method of multiplication other than fission or cell division. This group is divided into subgroups: the Schizophycee or blue-green alge, and the Schizomycetes or bacteria. The cells of the former contain chlorophyll or “ leaf green,’’ while the cells of the bacteria

Fic. 3. To illustrate the close relationship of the bacteria to the blue-green alge. The figures to the left (A) are blue-green alge, those to the right (B) bacteria. Those forms most closely resembling each other are lettered alike.

A, blue-green alge. a, Aphanocapsa. 6, Merismopedia. c, Gleotheca. d, Spirulina. e, Phormidium. f, Nostoc. (All adapted from West.)

B, bacteria. a, Micrococcus. }, Sarcina. c, Bacillus. d, Spirillum. e, Bacillus in chains. jf, Streptococcus.

are devoid of this pigment. The bacteria are to be studied, inasmuch as they contain so many forms of economic importance. '

The group Algz includes the seaweeds, pond scums, water silks, and similar forms. None of them are considered further. The group of Fungi differs from the Alge in the absence of chlorophyll and includes the toadstools, puffballs, mushrooms, smuts, rusts, mildews, yeasts, and molds. Only the two groups last mentioned are included in the scope of bacteriology.

The following classification may assist in getting a clear idea

POSITION OF MICROORGANISMS 15 of the position of the plant groups to be considered. These are given in boldface type, the others in italics.