AETIOLOGY OF TITBKROULOSIS 
201 
their alveolar spreading could already be plainly recognized by the naked eye. 
They did not appear sharply rounded off and circumscribed, but embraced 
mostly the centre of a lobulus. As the single alveoli were filled with a caseous 
mass and hence appeared as fine whitish little points, they had a dull fine-grained 
appearance, and on their border the white-yellowish little points of the caseous 
alveoli showed themselves very plainly against the dark, greyish-red circle. 
The largest tuberculous knots embraced an entire lobulus and sometimes ran to¬ 
gether into neighboring knots, in this manner forming larger, thickened, white- 
yellowish places in the lung which repeated completely the appearance of cas¬ 
eous pneumonia. The spontaneous tuberculosis occurring in rabbits and guinea 
pigs also shows in the structure of the primary tuberculous knots the conduct 
just described, namely, the alveolar spreading of the tuberculous process. This 
circumstance, therefore, confirms the view already expressed, that the spontane¬ 
ous tuberculosis of these animals is almost exclusively an inhalation tuberculosis. 
The rats and mice which were killed had very numerous little grey knots 
to the size of a hemp seed in the lungs, many of -which possessed a white- 
yellowish centre, yet the caseous degeneration was by far not so advanced as 
in the lungs of the guinea pigs and rabbits. In the spleen of the rats and 
mice also, only single grey knots were found. These animals, as has already 
been often made prominent, are far less sensitive to tuberculosis, the single 
tubercles develop in them much more slowly, and the further spread of the 
tuberculosis to other organs does not occur so easily. 
Also microscopically the tubercles arising from inhalation of pure cul¬ 
tures resemble completely the genuine tubercles in the arrangement of the 
epithelioid cells, the giant cells, and the contents in tuberculous bacilli. In 
order to prove the infectious properties of the same, twenty-two guinea pigs 
were inoculated subcutaneously in the abdomen with tubercles from various 
organs, as well from several guinea pigs as from rabbits and from the lung 
of a rat and of a mouse. These without exception were very soon attacked by 
swelling of the inguinal glands on the side of the inoculation, became ema¬ 
ciated and died in course of five to eight weeks of tuberculosis. 
If we look over all the experiments with pure cultures we reach the fol¬ 
lowing results: 
Those animals which belong to species easily susceptible to tuberculosis, 
namely, guinea pigs, rabbits, field-mice and cats, became tuberculous without 
exception in consequence of the infection with tuberculous bacilli. The num¬ 
ber of these animals amounts to two hundred and seventeen (ninety-four 
guinea pigs, seventy rabbits, nine cats and forty-four field mice). A number 
of animals for counter experiments, treated in like manner with indifferent 
liquids, and kept under the same conditions, on the contrary, without excep¬ 
tion, remained free from tuberculosis. Of the less susceptible animals, as a 
result of a simple subcutaneous inoculation, only domestic fowls, and, more¬ 
over, only half of those inoculated, became tuberculous. But even dogs, rats 
and white mice, which are usually very slightly susceptible to tuberculosis, 
could not withstand the infection with large quantities of purely cultivated 
tuberculous bacilli, and also without exception, became tuberculous. 
The various methods of infection used had the same effect with the pure 
