Bacteriology.—Although Leeuwenhoeck discovered the bacterium in 1668-1675, up to 100 years ago disease and death were largely regarded as dispensations of Providence, and with fatuous resignation were accepted as inevitable. The microscope and the study of bacteriology, however, have revealed to us the presence of minute living organisms or germs, which are everywhere around us, infesting the air, the earth, the water, our food, our bodies, and all organic matter in countless millions. These infinitely small beings multiply with a rapidity and fecundity that bewilders the imagination. Their method of multiplication is by fissiparism—that is to say, each splits into two independent beings that separate and afterwards lead independent lives. It is said that there is one species in which not more than six or seven minutes are required for the division to take place. A single individual might consequently produce more than a thousand offspring in an hour, more than a million in two hours, and in three hours more than the number of inhabitants on the globe. They are known as micro-organisms, of which the bacteria are the most important. The bacteria are further divided into species, and names are given them to distinguish the different forms. The little rod-shaped ones are called bacilli: the spheroidal ones micrococci or cocci. If they cling together in chains they are called streptococci; if of a spiral or corkscrew form they are called spirallae. The curved bacilli are called “comma” bacilli, from their resemblance to the punctuation mark of that name. The presence of peculiar forms of these bacteria in diseases has so suggested the relation of cause and effect as to have given rise to the so-called “germ theory” of disease. Now we know with reasonable certainty that cholera, diphtheria, typhoid fever, whooping cough, mumps, cerebro-spinal meningitis, pneumonia, tuberculosis, hydrophobia, and many other diseases have each its specific cause in the form of a microbe.
BACILLUS OF TUBERCULOSIS IN SPUTUM.
BACILLUS OF DIPHTHERIA (KLEBS-LOEFFLER).
FIG. 176.
BACILLUS OF TYPHOID FEVER.
(Photo-Micrographs, 1,000 diam., by William M. Gray, M. D.)