aft 
_by the gradual changes which they themselves induce. Thusin the 
teria more adapted to the conditions now prevailing get a foothold, 
Aer SaaS a ics Bea esata i ak cn ee ae 
‘ oy hes : te * Besa) ess “ f e A eS a.) 
510 REPORT OF THE COMMISSIONER’ ULTURE, — 
N59 ‘as Pye. 
place the bacteria, which are in reality the cause of the disease, may — 
be present only at a certain stage of the disease, being subsequently 
destroyed by the cells as the lungs heal, or giving away to accidental 
forms as the disease progresses. We must bear in mind with refer- | 
ence to the second alternative that pathogenic bacteria must suffer 
early stages they undoubtedly live and multiply inthe exudate which — 
is contained in the alveoli. When this becomes more and more con-— 
solidated, and as the ultimate bronchi are occluded by exudate, the 
bacteria are being deprived of nutriment and oxygen. The tissue 
dies, and with it the bacteria originally causing its death ; other bac- 
until the entire lung becomes a prey to many kinds of bacteria. a 
A well-known illustration may be cited In support of these asser- 
tions. The tubercle bacilli, which may be seén in sections of young 
tubercles, can not, as arule, be found in the caseous mass which forms 
later on in the center of the enlarging tubercle. Inoculations of 
blood serum with such material are apt to prove failures, and if it 
were not that inoculation into guinea pigs is almost invariably suc- _ 
cessful we might presume that the bacilli had perished. The factis, 5 
the bacilli, finding no suitable conditions of growth in the caseous 
mass, would perish if it were not that they have the capacity to form | 
spores under such circumstances. These spores, which may fail to | 
germinate on blood serum, find a more suitable medium in guinea 
pigs, where they soon give rise to-a generalized tuberculosis. 
The problem to be solved, therefore, was to isolate the specific bac- 
teria which are the cause of the disease from the rest. The method 
pursued was to introduce minute bits of diseased lung tissue beneath 
the skin of rabbits and mice. If the specific bacteria are present 
they will in all probability cause the death of the inoculated ani- 
mals. They will then be found in one or more of the internal organs, 
from which they can be obtained free from the other bacteria. These 
will remain restricted to the place where they were deposited. This 
method of obtaining disease germs has been used by other investi- 
gators, more particularly by Schiitz, in the study of swine plague in 
Germany, and more recently in investigations of infectious pneumo- , 
nia in horses. A résumé of this work on the bacterium causing 
swine plague has been given in the preceding report of the Bureau in 
connection with the preliminary investigations made last year of 
American swine plague. The facts in the case are briefly as follows: 
It was found that in the majority of cases, when bits of diseased lung 
tissue were placed beneath the skin of rabbits and mice (or simply 
rubbed into any slight prick made on the ear with a lancet), a scepti- 
ceemia appeared with which the bacteria described in the preceding 
report were always and exclusively associated. Rabbits are more 
susceptible than mice, and die in from one to four days after inocula- ~ 
tion. By thismeans pure cultures of the same bacteria were obtained 
from most of the cases reported in the preceding pages. This was 
therefore the only microbe present which was capable of destroying 
the smaller experimental animals. 
It may be argued that bacteria obtained in this way may be acci- 
dentally present in the diseased lung tissue, and that the bacteria 
which are the real cause may not produce any disease whatever in 
the experimental animals. Without enterimg at present into any 
detailed statement of the other arguments in favor ot this bacterium 
as the cause of swine plague we may state that most of the bacteria | 
