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TUBERCULOSIS.                          221

The tubercle bacillus seems to require a considerable
amount of oxygen for its development. It is also pecu-
liarly sensitive to temperatures, not growing at a tem-
perature below 29° C. or above 42° C. Temperatures
above 75° C. kill it after a short exposure.

The tubercle bacillus does not develop well in the
light, and when its virulence is to be maintained should
always- be kept in the dark. Sunlight kills it in from
a few minutes to several hours, according to the thick-
ness of the mass exposed to its influence.

The widespread character of tuberculosis at one time
suggested the idea that tubercle bacilli were ubiquitous
in the atmosphere, that we all inhaled them, and that it
was only our vital resistance that prevented us all from
becoming its victims.

Cornet must be given the credit of having shown that
such an idea is untrue, and that tubercle bacilli only
exist in the atmospheres frequented by consumptives.
His experiments were made by collecting dusts from
numerous places—streets, sidewalks, houses, rooms, walls,
etc. Injecting them into guinea-pigs, whose constant
susceptibility to the disease makes them a very delicate
reagent for its detection, Cornet showed the bacilli to be
present only in the dust with which pulverized sputum
was mixed, and found such infectious dust to be most
common where the greatest carelessness in respect to
cleanliness prevailed.

Our present knowledge of the life-history of the tubercle
bacillus, by showing its indisposition to multiply outside
the bodies of animals, the deleterious influence of sun-
light upon it, the absence of positive permanent forms,
and its sensitivity to temperatures beyond a certain range,
confirms all that Cornet has pointed out, and shows us
why the expectoration of millions of consumptives has
not rendered our atmospheres pestilential.

As long as tuberculosis exists among men or cattle, it
shows that the existing hygienic precautions are insuf-