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DIPHTHERIA,                            291

Upon potato the bacillus develops only when the reac-
tion is alkaline. The potato-growth is not characteristic.
Welch and Abbott always secured a growth of the organ-
ism when planted upon potato, but do not mention the
reaction of the medium they employed.

Milk is an excellent medium for the cultivation of the
Bacillus diphtherias, and is possibly at times a means of
infection. Litmus milk is an excellent medium for ob-
serving the changes of reaction brought about by the
growth of the bacillus. At first the alkalinity, which
is always favorable to the development of the bacillus,
is destroyed by the production of an acid. When the
culture is old the acid is replaced by a strong alkaline

Palmirski and Orlowskil assert that the bacillus pro-
duces indol, but only after the third week. Smith, how-
ever, came to a contrary result, and found that when
diphtheria bacillus grew in the dextrose-free bouillon
that he recommends no indol was produced.2

Diphtheria as it occurs in man is generally a disease
characterized by the formation of a pseudomembrane
upon the fauces. It is a local infection, due to the
presence and development of the bacilli in the pseudo-
membrane, but is accompanied by a general toxemia
resulting from the absorption of a violently poisonous
substance produced by the bacilli. The bacilli are found
only in the membranous exudation, and most plentifully
in its older portions. As a rule, they do not distribute
themselves through the circulation of the animal, though
at times they may be found in the heart's blood.

The most malignant cases of the disease are thought
to be due to pure infection by the diphtheria bacillus,
though such cases are more rare than those in which the
Streptococcus pyogenes and Staphylococcus aureus and
albus are found in association with it.

In a series of 234 cases carefully and statistically studied

1  Centralblf. Bakt. u. Parasitenk., Mar., 1895.

2 Jour, of Exper. Med., vol. ii., No. 5, Sept., 1897, p. 546.