In 1836 Chevreuil and Pasteur showed that putrefaction did not occur in meat protected from contamination. In 1837 Caignard-Latour, in France, and Schwann, in Germany, independently showed that alcoholic fermentation in beer and wine is due to the growth of a microscopic plant, the yeast, in the fermenting wort. C. J. Fuchs described the organism which is commonly called the “blue milk bacillus” in 1841 and conjectured that the souring of milk was probably bacterial in origin. It remained for Pasteur to prove this in 1857. During the following six or seven years Pasteur also proved that acetic acid fermentation, as in vinegar making, butyric acid fermentation (odor of rancid butter and old cheese) and the ammoniacal fermentation of urea, so noticeable around stables, were each due to different species of bacteria. Pasteur also, during the progress of this work, discovered the class of organisms which can grow in the absence of free oxygen—the anaërobic bacteria. There is no question that Pasteur from 1857 on did more to lay the foundations of the science of bacteriology than any other one man. Influenced by Pasteur’s work von Hesseling, in 1866, stated his belief that the process of cheese ripening, like the souring of milk, was associated with the growth of fungi, and Martin also, in 1867, stated that cheese ripening was a process which was akin to alcoholic, lactic and butyric

fermentations. Kette, in 1869, asserted the probability of Pasteur’s researches furnishing a scientific basis for many processes of change in the soil. In 1873 Schlösing and Müntz showed that nitrification must be due to the action of microörganisms, though the discovery of the particular ones remained for Winogradsky in 1889. Thus the belief that fermentation and putrefaction are due to microörganisms was as well established by the early eighties of the last century as that similar organisms are the causes of infectious diseases.

STUDY OF FORMS.

An important part of the scientific knowledge of living organisms is dependent on a study of their forms and relationships. As has been stated, Leeuwenhoek considered bacteria to be “animalcules” because they showed independent movement. But little attention was paid to the natural history of these animalcules for nearly a hundred years after Leeuwenhoek. During the last quarter of the eighteenth century, however, workers

busied themselves chiefly with the discovery and description of new forms. Among these students were Baron Gleichen, Jablot, Lesser, Reaumur, Hill and others. Müller, of Copenhagen, in 1786 published the first attempt at classification, a most important step in the study of these organisms. Müller introduced the terms Monas, Proteus and Vibrio, which are still in use. Ehrenberg, in his work on Infusoria, or the organisms found in infusions, published in 1838, introduced many generic names in use at present, but still classed the bacteria with protozoa. Joseph Leidy, the American naturalist, considered that the “vibrios” of previous writers were plants and not “animalcules.” He seems to have been the first to have made this distinction (1849). Perty (1852) recognized the presence of spores in some of his organisms. Ferdinand Cohn (1854) classed the bacteria among plants. Nägeli (1857) proposed the name “Schizomycetes” or “fission fungi,” which is still retained for the entire class of bacteria. Cohn in the years 1872–1875 established classification on a modern basis and added greatly to the knowledge of morphology and natural history of bacteria. He described spore formation and the development of spores into active bacteria, and showed the close relationships as well as differences between the bacteria and the lower algæ. Robert Koch was a pupil of Cohn.

An examination of the accompanying chronological table will show how the investigations and discoveries in connection with “spontaneous generation,” the “contagium vivum” theory and putrefaction and fermentation must have been mutually suggestive:

1546.Fracastorius, disease germs theory and direct and indirect contagion.
1671.Kircher, “contagium vivum” theory.
1675.Leeuwenhoek, first saw bacteria, “animalcules.”
1701.Andry, “animalcules” cause of diseases.
1718.Lancisi, “animalcules” cause of malaria.
1749.Needham, described development of organisms in water around barley grains.
1762.Plenciz, arguments for “living cause” theory and that “animalcules” cause putrefaction.
1768.Bonnet, suggested that probably Needham’s organisms came from germs in the liquid.
1776.Spallanzani, boiled and sealed infusions.
1786.Müller, first classified “animalcules.”
1787.Wollstein, glanders pus infectious.
1795–1798.Jenner, vaccination against smallpox.
1797.Viborg, transmitted glanders repeatedly.
1807.Prevost, grain rust, Puccinia graminis. The first instance of a microscopic plant organism shown to be the cause of a disease in a higher plant.
1810.Appert, directions for “canning.”
1822.Gaspard, infectiousness of material from wounds.
1834.Renucci, itch—itch mite (Sarcoptes scabiei).
1835.Paget and Owen, Trichina spiralis.
1836.Schultze, air through acid to kill “germs.”
1837.Chevreuil and Pasteur, protected meat did not putrefy; suggested wound infection due to entrance of germs from without.
1837.Caignard-Latour, Schwann, alcoholic fermentation—yeast.
1837.Schwann, air through heated tubes to kill germs.
1837.Bassi, muscardine of silkworms, Botrytis bassiana. The first instance of a microscopic plant organism shown to be the cause of a disease in an animal.
1838.Boehm, cholera, saw organisms in stools (not the cause).
1838.Dubini discovered Ankylostoma duodenale.
1838.Ehrenberg, study of forms.
1839.Schönlein, Favus, Achorion schoenleinii.
1839–41.Berg, Thrush, Oidium albicans.
1840.Henle, theory of contagious diseases.
1841.Fuchs, bacterial cause of blue milk.
1842–43.Gruby, Herpes tonsurans, Trichophyton tonsurans.
1843.Klencke, inoculations of tuberculous material into rabbit.
1843.Holmes, puerperal fever contagious.
1845.Liebert, a potato rot, Peronospora infestans.
1846.Leidy, Joseph (American Naturalist), Trichina spiralis in pork.
1846.Eichstedt, Pityriasis versicolor, Microsporon furfur.
1847.Semmelweiss, recommended disinfection to prevent puerperal fever. Not followed.
1849.Leidy, considered “vibrios” to be plants.
1849.Pollender, Anthrax, saw rods in blood.
1850.Davaine and Rayer, Anthrax, saw rods in blood.
1851.Griesinger, Egyptian chlorosis, Ankylostoma duodenale.
1851.Bilharz, Bilharzia disease, Schistosomum hematobium.
1852.Kückenmeister, tapeworm, Tænia solium.
1852.Perty, saw spores in bacteria.
1854.Cohn, classed bacteria as plants.
1855.Cohn, disease of flies, Empusa muscæ.
1857.Nägeli, named bacteria, Schizomycetes.
1857.Pasteur, lactic, acetic, butyric acid fermentation.
1860.Zenker, Trichinosis, Trichinella spiralis.
1861.Pasteur, disproof of spontaneous generation.
1863.Davaine, transmitted anthrax by blood injections.
1865.Pasteur, Pebrine of silkworms, Nosema bombycis. The first instance of a protozoan shown to be the cause of a disease in a higher animal.
1865.Villemin, repeatedly transmitted tuberculosis to rabbits.
1865.Lister, introduced antisepsis in surgery.
1860.Rindfleisch, Pyemia, organisms in the pus.
1866.Von Hesseling, cheese ripening.
1867.De Martin, cheese ripening akin to alcoholic fermentation.
1869.Kette, Pasteur’s researches scientific basis for many processes in the soil.
1871.Klebs, Pyemia, organisms in the pus.
1872.Bollinger, spores in anthrax.
1872–75.Cohn, definite classification.
1873.Obermeier, recurrent fever, Spirochæta obermeieri.
1873.Schlösing and Münz, nitrification due to organisms.
1875.Lösch, amebic dysentery, Amœba coli.
1875–76.Tyndall, germs in the air.
1876.Robert Koch, anthrax, Bacillus anthracis. The first instance of a bacterium shown to be the cause of disease in an animal.
1877.Bollinger, actinomycosis, Actinomyces bovis (Streptothrix bovis).
1877.Weigert, used anilin dyes for staining.
1877.Woronin, cabbage disease, Plasmodiophora brassicæ. The first instance of a protozoan shown to be the cause of a disease in a plant.
1878.Koch, wound infections, bacterial in origin.
1881.Koch, gelatin plate cultures, Abbé, improvements in the microscope.

CHAPTER I.
POSITION—RELATIONSHIPS.

Bacteria are considered to belong to the plant kingdom not because of any one character they possess, but because they most nearly resemble organisms which are generally recognized as plants. While it is not difficult to distinguish between the higher plants and higher animals, it becomes almost, if not quite, impossible to separate the lowest, forms of life. It is only by the method of resemblances above mentioned that a decision is finally reached. It has even been proposed to make a third class of organisms neither plants nor animals but midway between in which the bacteria are included, but such a classification has not as yet been adopted.