ficially dyed with anilin, except those of
tubercle and anthrax. One species is stained readily with a dye that
leaves another unaltered. Thus we are enabled in the laboratory to
determine whether the bacilli found in sputum, for example, are from
tubercle or are the bacteria of decomposition.

From what I have said of the tubercle bacillus, it would seem
thoroughly demonstrated that it is the cause of tubercle in these
animals. But we must walk cautiously here. These are not human beings,
who know that like results would follow their inoculation. The animals
used by Koch are animals very subject to tubercle.

We must, from the very nature of our environment, be constantly
inhaling these germs as we pass through the wards of our hospitals;
yes, they are floating in the air of our streets and dwellings. It
becomes necessary then for us to inquire: If bacteria cause disease,
in what manner do they produce it? The healthy organism is always
beset with a multitude of non-pathogenic bacteria. They occupy the
natural cavities, especially the alimentary canal. They feed on the
substances lying in their neighborhood, whether brought into the body
or secreted by the tissues. In so doing they set up chemical changes
in their substances. Where the organs are acting normally these fungi
work no mischief. The products of decomposition thus set up are
harmless, or are conveyed out of the body before they begin to be
active.

If bacteria develop to an inordinate degree, if the contents of organs
are not frequently discharged, fermentative processes may be set up,
which result in disease. Bacteria must always multiply and exist at
the expense of the body which they infest, and the more weakened the
vital forces become, the more favorable is the soil for their
development.

Septicaemia is caused by the absorption of the products of
putrefaction, induced before bacteria can multiply inside or outside
the body. Bacteria must find a congenial soil. The so-called cholera
bacillus must gain access to the intestinal tract before it finds
conditions suitable to colonization. It does not seem to multiply in
the stomach or in the blood, but once injected into the duodenum
develops with astonishing rapidity, and the delicate epithelial cells
of the villi become swollen, soften and break down, exposing the
mucosa.

It has been shown that _bouillon_ in which Loeffler's diphtheria
bacillus has grown, and which has been passed through unglazed