The Atlantic Seaboard


EARLY BACTERIOLOGIC METHODS
   We must keep the times in mind and realize that the methods of
bacteriology in the eighties, nineties, and even later were primitive and
inexact. Bacteriology and its kindred branch immunology remained
among the weakest of the descriptive sciences until well into the twen-
tieth century. Technics were simple and special skills were not needed;
only slowly did bacteriology become a highly detailed science.
   To obtain pure cultures of a single species for study, the progressive
dilution method of Pasteur and of Lister gradually gave place to the
solid gelatin media of Koch on glass plates; the messy liquefiers of
this method were eliminated when the relatively indigestible agar-
agar,4 still unbelievably valuable, came into use. The continuing boon
of the cotton plug for tubes and flasks and the circular petri dish for
pouring dilutions are to this day our simple universal aids. Common
dyes and special stains such as the Gram and acid-fast gave evidence of
differences in chemical structure. Differences in physiology as shown
by the action of a microbe on a single carbohydrate with the production
of acids or acid and gas, when this ingredient is added to the medium,
led us almost at once into biochemistry, where Pasteur started. Since
bacteria as disease-inciting agents were the prominent ones in the
awakening of our minds, experimental animals were used early both as
a means of eliminating contaminating organisms (pneumonia sputum
into mice) and as the models in determining etiology by fulfilling the
Henle-Koch postulates.
  This mode of study immediately took the bacteriologist over into
pathology; soil, dairy, and industrial bacteriology opened still other
doors. Calibrated pipettes of the chemist fostered quantitative methods,
and physical and chemical agents such as steam in autoclaves under
pressure and toxic salts such as those of mercury were employed for
sterilization and disinfection. Artificial means of building up active
resistance, so-called vaccination, came early as in smallpox by Jenner,
1798, and in rabies by Pasteur, 1883-85. Artificial passive immunity
by developing the active process in the body of another animal, as for
example by the injection of repeated doses of the exotoxins of Bacillus
diphtheriae into a horse and the use of the antitoxin produced by the
horse as a therapeutic agent in the sick person, came in 189o and later.
  The antigen-antibody reactions that have proved so valuable in estab-
lishing specific relationships between a given microbe and a particular
disease also became available later, i888-i9oi. From i888, when Nut-


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