168 THE MICROSCOPE. 
an atmosphere thickened with coal-dust, and the roots of the lungs 
were more closely examined immediately after death, the lymphatic 
canals appeared as gray lines, just as if India ink had been artifici- 
ally injected. The liquid contents of the canals could be moved 
hither and thither by stroking and pressing, more easily, of course, 
towards the lymphatic glands than in the opposite direction, because 
of the opposition offered by the imperfect valvular apparatus. 
On closer examination, the gray contents was found to consist 
of fine granules of coal, partly free, partly inclosed in the cells, of 
exactly the same appearance as that in the lung parenchyma. From 
the above experiments, the following was deduced: From the 
surface of the alveoli the coal-dust and soot force their way into the 
parenchyma of the lung; there it must be supposed there exists free 
communication, although the passages cannot be demonstrated. 
But that these passages may be traced, was later shown by 
Klein. (Elements of Histology, third edition, 1884.) Between the 
flattened, transparent epithelium cells lining the alveoli are minute 
openings, “stomata,” leading from the cavity of the air-cells into 
the lymph-lacunze of the alveolar wall. These ‘‘ stomata” are more 
distinct during expansion, 7 e., inspiration, than in the collapsed 
state. Inspiration, by its expanding the lungs, and consequently 
also the lymphatics, greatly favors absorption. Through these 
“ stomata,” and also through the interstitial cement substance of the 
lining epithelium, may penetrate particles, such as soot from a 
smoky atmosphere,pigment artificially inhaled, cellular elements, such 
as mucous or pus corpuscles, and even germs that have been carried 
into the alveoli from the bronchi by natural inspiration. They may then 
pass into the lymphatic vascular system, close to its finest roots (the 
lymph-canaliculi of Recklinghausen), which, of course, cannot be 
represented. From here they pass into the lymphatic vascular 
capillaries, and are gathered particularly where several lung alveoli 
meet, chiefly at the point of transmission of the infundibula into the 
alveolar passages. Just here the dust particles accumulate. The 
‘lymphatic vascular systems mingle in the sub-pleural, but especially 
in the peri-bronchial and peri-vascular tissues; and through their 
channels the dust particles move, and are carried into the bronchial 
and tracheal-lymphatic glands, and there deposited. 
As Slavjansky proved (Virchow’s Archiv., Vol. XLVIII, page 
326), lymphoid cells appeared in the lung alveoli after experimental 
inhalations of dust, in which especially cinnabar, also ultramarine, 
indigo and coal dust were used, or with animals compelled to 
remain for a considerable time in a dust-laden atmosphere. These 
