The Fundamentals of Bacteriology. Charles Bradfield Morrey
… … . … .Corynebacterium
II—Gram negative. Rods sometimes form threads. Characteristic honey-like growth on potato … … . … .Pfeifferella
FF—Cells staining unevenly but with branched or filamentous forms at certain stages. Never acid fast. Not animal parasites.
G—Metabolism simple, growth processes involving oxidation of alcohol or fixation of free N (latter in symbiosis with green plants).
H—Cells minute. Symbiotic in roots of legumes … … . … .Rhizobium
HH—Oxidizing alcohol. Branching forms common … … . … .Acetobacter
GG—Not as G. Proteus-like colonies.
H—Not attacking carbohydrates … … . … Zopfius
HH—Fermenting glucose and sucrose at least … … . … .Proteus
EE—Regularly formed rods.
F—Metabolism simple, growth processes involving oxidation of C, H, or their simple compounds or the fixation of free N.—NITROBACTERIACEÆ.
G—Fixing N or oxidizing its simple compounds.
H—Fixing N, cells large, free in soil … … . … Azotobacter
HH—Oxidizing N compounds.
I—Oxidizing NH4 compounds … … . … Nitrosomonas
II—Oxidizing nitrites … … . … Nitrobacter
GG—Not as G.
H—Oxidizing free H … … . … Hydrogenomonas
HH—Oxidizing simple C compounds, not free H.
I—Oxidizing CO … … . … Carboxydomonas
II—Oxidizing CH4 … … . … Methanomonas
FF—Not as F.
G—Flagella usually present, polar—PSEUDOMONADACEÆ … … . … Pseudomonas
GG—Flagella when present peritrichic—BACTERIACEÆ
H—Parasitic forms showing bi-polar staining … … . … .Pasteurella
HH—Not as H.
I—Strict parasites growing only in presence of hemoglobin … … . … Hemophilus
II—Not as I.
J—Water forms producing red or violet pigment.
K—Pigment red … … . … Erythrobacillus
KK—Pigment violet … … . … Chromobacterium
JJ—Not as J.
K—Plant pathogens … … . … Erwinia
KK—Not plant pathogens.
L—Gram +, forming large amount of acid from carbohydrates, sometimes CO2, never H … … . … Lactobacillus
LL—Gram −, forming H as well as CO2 if gas is produced … … . … Bacterium
DD—Endospores present—BACILLACEÆ
E—Aerobes, rods not swollen at sporulation … … . … .Bacillus
EE—Anaërobes, rods swollen at sporulation … … . … .Clostridium
PART II.
PHYSIOLOGY.
CHAPTER VI.
GENERAL CONDITIONS FOR GROWTH.
OCCURRENCE.
Bacteria are probably the most widely distributed of living organisms. They are found practically everywhere on the surface of the earth. Likewise in all surface waters, in streams, lakes and the sea. They occur in the air immediately above the surface, since they are carried up mechanically by air currents. They cannot fly of themselves. There is no reason to believe that any increase in numbers occurs to an appreciable extent in the air. The upper air, for example, on high mountains, is nearly free from them. So also is the air over midocean, and in high latitudes. As a rule, the greater the amount of dust in the air, the more numerous are the bacteria. Hence they are found more abundantly in the air in cities and towns than in the open country. The soil is especially rich in numbers in the upper few feet, but they diminish rapidly below and almost disappear at depths of about six feet unless the soil is very porous and open, when they may be carried farther down. Hence the waters from deep wells and springs are usually devoid of these organisms. In the sea they occur at all levels and have been found in bottom ooze dredged from depths of several miles. It is perhaps needless to add that they are found on the bodies and in the alimentary tract of human beings and animals; on clothing, utensils; in dwellings, stables, outhouses, etc. From one-fourth to one-half of the dry weight of the feces of animals and men is due to the bacteria present. The urine is practically free from them in health.
While bacteria are thus found nearly everywhere, it is an entirely mistaken idea to suppose that all are injurious to man. As a matter of fact, those which are dangerous are relatively few and are for the most part found only in close association with man. Most bacteria are harmless and the vast majority are beneficial or even essential to man’s existence on the earth. These facts must be constantly borne in mind, and it is hoped that the pages which follow will make them clear.
In order that any organism may thrive there are a number of general environmental conditions which must be fulfilled. These conditions vary more or less for each kind of organism. Bacteria are no exception to this general rule. These conditions may be conveniently considered under the general heads of moisture; temperature; light; oxygen supply; osmotic pressure; action of electricity; of Röntgen and radium rays; pressure; mechanical vibration; and chemical environment, including the reaction of the medium, the effect of injurious chemicals, and especially the food requirements of bacteria. For each of these conditions there is a maximum, meaning the greatest amount of the given condition which the organism can withstand, a minimum, or the least amount, and an optimum or that amount which is most favorable for development. Further, there might be distinguished a maximum for mere existence and a lower maximum for development; also a minimum for mere existence and a higher minimum for development. These maxima, minima, and optima for bacteria have been determined with exactness for only a very few of the general conditions and for comparatively few kinds.
MOISTURE.
The maximum moisture is absolutely pure water, and no organism can thrive in this alone owing to the factor of too low osmotic pressure and to the further factor of absence of food material. There are many bacteria which thrive in water containing only traces of mineral salts and a large class whose natural habitat is surface water. These “water bacteria” are of great benefit in the purification of streams. They are as a class harmless to men and animals. Some of the disease-producing bacteria like Bacterium typhosum (of typhoid fever) and Vibrio choleræ (of Asiatic cholera) were undoubtedly originally water bacteria, and it is rather striking that in these diseases conditions are induced in the intestine (diarrheas) which simulate the original watery environment. The minimum moisture condition is absolute dryness, and no organism can even exist, not to say develop, in such a condition