AETIOLOGY OF TUBERCULOSIS. 
209 
have got into the lungs by inhalation, into the skin by wounds, into the intestinal 
canal by swallowing, in their further conduct in the body, we see that they often 
remain for a long time—sometimes even permanently—in the place of their first 
establishment. From herds of epithelioid cells they form liitle knots which enclose 
giant cells, and regularly from the centre out, fall victims to coagulation-necrosis. 
The appearances which are conditioned upon the gradual growth of such a herd, 
and the regressive changes which always keep step with it, have been described 
in detail in a former section. The first sign of the spreading of the tuberculous 
process into the neighboring regions is the formation of similar knots in the neigh¬ 
borhood of the primary herd. The way, also, in which the migration of the bacilli 
from the first herd to the place where the secondary knots arise, is to be conceived, I 
have also already suggested. The following appears to me to be the simplest 
explanation of this proceeding. The tuberculous bacilli, since they possess no 
motion of their own, can only be moved along by elements possessing the power 
of motion, or by currents of liquid. But since the tuberculous knots have no 
vasal and one cannot see how other liquids, which are in motion, can get into the 
tuberculous herd and sweep away bacilli from them, nothing remains but the wan¬ 
dering cells, which according to experience, act the same part in other disease- 
producing bacteria, which those elements perform, that provide for the transport 
of the bacilli. The cell, laden with a bacillus only goes on until, under the influ¬ 
ence of the parasite, it loses its power of motion. On the spot where the cell 
came to a stand-still, a new tuberculous knot must arise. In this manner groups 
of tubercles form, which melt, perish and cause destruction in the well-known 
manner. 
With the supposition that the wandering cells may be the bearers of the 
bacilli, we see in the most natural manner the connection with the farther ex¬ 
cursions which the tuberculous bacilli make in the body in almost all cases. 
When the wandering cell moves in the tissue-passages and must rely on its own 
power of motion, then the distance which it travels is only a short one and the 
newly arising infectious herd must lie in the neighborhood of the point of de¬ 
parture. But as soon as the wandering cells move in the lymph-vessels and 
the lymph-stream comes to their help in tlieir movement, then they travel 
greater distances, as is seen not seldom in the tubercles spreading themselves 
out in the course of the lympli-vessels. But very often then the tuberculous 
bacilli are swept away still farther in the lympli-vessels and led into the nearest 
lymph-glands, where in like manner as in the first place of infection they call 
forth the formation of knots and caseous degeneration. The changes condi¬ 
tioned upon this in the gland-tissue appear usually to hinder a further progress 
of the bacilli by the way of lymph-passages. But by this no insurmountable 
barrier is placed in the way of the progress of the bacilli. They can, under 
special conditions, get into the stream of the blood. This happens when, as 
Ponfick has shown, the tuberculosis attacks the thoracic duct, and reaches the 
interior of the same ; the tuberculous bacilli are then led direct from the lymph- 
stream into the blood-stream. 
A second, and moreover the most frequent cause for the entrance of tuber¬ 
culous bacilli into the blood, has been discovered by Weigert. This is the 
formation of tuberculous knots in the walls of veins and the breaking through 
of the perishing knots into the lumen of the vasa. 
