AETIOLOGY OF TUBERCULOSIS. 
20T 
the tuberculous bacilli, is favored. If one makes clear to himself the necessity of 
such favorable moments for the entrance of the tuberculous bacilli, then it can no 
longer appear so striking that many persons, in spite of constant association with 
consumptives, are not infected, while others are plainly infected at the first oppor¬ 
tunity, and still others after they have been exposed to the infection for a long time 
finally, nevertheless, fall a victim to the same. In the case of the first mentioned 
nothing helped the tuberculous bacilli, which were doubtless often enough inhaled, 
and they were therefore removed again from the respiratory passages ; the second 
had from the beginning a defective spot in their respiratory organs, on which the 
bacilli were able to fasten themselves, and it was only necessary that the infectious 
germ should reach just this spot; the last mentioned not until later had such a 
defect and lost by means of it to a certain extent their immunity from tuberculosis. 
The difficulties which stand in the way of the establishment of the tuberculous 
bacilli in the upper air passages are greater and this fact explains the rare cases 
in which they primarily become diseased. 
Since by far the greatest number of cases of tuberculosis begin in the lungs, it 
is to be supposed that the infection in all these cases has taken place in the 
manner just suggested by the inhalation of phthisic sputum dried and made into 
dust. On account of the immence production of the infectious material and on 
account of the frequent contact in which it must come with other parts of the hu¬ 
man body, it is nevertheless not improbable that the infection can take place 
from other parts than the lungs. So I would say, that the primary attacks of 
lymph glands lying on the surface arising from scratches, skin-eruptions, etc., into 
which tuberculous bacilli have accidentally entered, have formed the entrance gate 
for the infection, from whence the bacilli have been carried farther and have got 
into the lymph glands, then when the original point of infection has been healed, 
it appears as if the disease-process had developed primarily in the glands. A 
number of cases in which in otherwise healthy human beings caseous lymph glands 
containing tuberculous bacilli were cut out from the back of the neck, I could not 
otherwise explain, than that they arose through infectionfrom scratches on the skin 
of the head. Since the excrement of consumptives not rarely contains tuberculous 
bacilli, the same is true in regard to the danger of infection from this as from the 
sputum, when there is opportunity for its drying and being scattered as dust. But 
this does not occur probably very often ; all the same thispossibility of spreading 
the infectious material is to be kept in view. 
The second principal source for the tuberculous bacilli, namely, tuberculosis of 
the domestic animals, appears not to have anything like the importance of the 
phthisic sputum. The animals, as is well known, produce no sputum, so that during 
their life no tuberculous bacilli get from them into the outer world by means of 
the respiratory passages. Also in the excrement of tuberculous animals tubercu¬ 
lous bacilli appear to be only exceptionally present. On the contrary, it is a fact 
that the milk of tuberculous animals can cause infection. With the exception of 
this one way, therefore, the tuberculous virus can only have effect after the death 
of the animal and can only cause infection by the eating of the meat. Aside from 
the probably only rarely occurring cases of direct infection, which can follow 
from coming in contact with tuberculous parts of the flesh of little wounds and 
exoriations of the skin, the reception of the infectious material will result in this 
