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Page 28
Hides and wool taken from dead animals invariably contained the spores
which could pass unharmed through some of the curing processes, and
were responsible for some of the cases in man. Owing to the
introduction of regulations which were based on the knowledge of the
cause of the disease and the life history of the organism, together
with the prophylactic inoculation devised by Pasteur, the incidence of
the disease has been very greatly lessened. Looking at the matter from
the lowest point of view, the money which has been saved by the
control of the disease, as shown in its decline, has been many times
the cost of all the work of the investigations which made the control
possible. It is a greater satisfaction to know that many human lives
have been saved, and that small farmers and shepherds have been the
chief sharers in the economic benefits. The indirect benefits,
however, which have resulted from the application of the knowledge of
this disease, and the methods of investigation developed here, to the
study of the infections more peculiar to man, are very much greater.
FOOTNOTE:
[1] The interesting analogy between fermentation and infectious
disease did not escape attention. A clear fluid containing in solution
sugar and other constituents necessary for the life of the yeast cells
will remain clear provided all living things within it have been
destroyed and those in the air prevented from entering. If it be
inoculated with a minute fragment of yeast culture containing a few
yeast cells, for a time no change takes place; but gradually the fluid
becomes cloudy, bubbles of gas appear in it and its taste changes.
Finally it again becomes clear, a sediment forms at the bottom, and on
re-inoculating it with yeast culture no fermentation takes place. The
analogy is obvious, the fluid in the first instance corresponds with
an individual susceptible to the disease, the inoculated yeast to the
contagion from a case of transmissible disease, the fermentation to
the illness with fever, etc., which constitutes the disease, the
returning clearness of the fluid to the recovery, and like the
fermenting fluid the individual is not susceptible to a new attack of
the disease. It will be observed that during the process both the
yeast and the material which produced the disease have enormously
increased. Fermentation of immense quantities of fluid could be
produced by the sediment of yeast cells at the bottom of the vessel
and a single case of smallpox would be capable of infecting
multitudes.
CHAPTER VI
CLASSIFICATION OF THE ORGANISMS WHICH CAUSE DISEASE.--BACTERIA: SIZE,
SHAPE, STRUCTURE, CAPACITY FOR GROWTH, MULTIPLICATION AND SPORE
FORMATION.--THE ARTIFICIAL CULTIVATION OF BACTERIA.--THE IMPORTANCE OF
BACTERIA IN NATURE.--VARIATIONS IN BACTERIA.--SAPROPHYTIC AND
PARASITIC FORMS.--PROTOZOA.--STRUCTURE MORE COMPLICATED THAN THAT OF
BACTERIA.--DISTRIBUTION IN NATURE.--GROWTH AND MULTIPLICATION.--
CONJUGATION AND SEXUAL REPRODUCTION.--SPORE FORMATION.--THE NECESSITY
FOR A FLUID ENVIRONMENT.--THE FOOD OF PROTOZOA.--PARASITISM.--THE
ULTRA-MICROSCOPIC OR FILTERABLE--ORGANISMS.--THE LIMITATION OF THE
MICROSCOPE.--PORCELAIN FILTERS TO SEPARATE ORGANISMS FROM A FLUID.--
FOOT AND MOUTH DISEASE PRODUCED BY AN ULTRA-MICROSCOPIC ORGANISM.--
OTHER DISEASES SO PRODUCED.--DO NEW DISEASES APPEAR?
The living organisms which cause the infectious diseases are
classified under bacteria, protozoa, yeasts, moulds, and
ultra-microscopic organisms. It is necessary to place in a separate
class the organisms whose existence is known, but which are not
visible under the highest powers of the microscope, and have not been
classified. The yeasts and moulds play a minor part in the production
of disease and cannot be considered in the necessary limitation of
space.
[Illustration: FIG. 17.--VARIOUS FORMS OF BACTERIA, _a_, _b_, _c_,
_d_, Round bacteria or cocci: (_a_) Staphylococci, organisms which
occur in groups and a common cause of boils; (_b_) streptococci,
organisms which occur in chains and produce erysipelas and more severe
forms of inflammation; (_c_) diplococci, or paired organisms with a
capsule, which cause acute pneumonia; (_d_) gonococci, with the
opposed surfaces flattened, which cause gonorrhoea. _e_, _f_, _g_,
_h_, Rod-shaped bacteria or bacilli: (_e_) diphtheria bacilli; (_f_)
tubercle bacilli; (_g_) anthrax bacilli; (_h_) the same bacilli in
cultures and producing spores; a small group of spores is shown. (_i_)
Cholera spirill�. (_j_) Typhoid bacilli. (_k_) Tetanus bacillus;
_i_, _j_, _k_ are actively motile, motion being effected by the small
attached threads. (_l_) The screw-shaped spirochite which is the cause
of syphilis.]
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