RESPIRATORY SPACES OF THE LUNGS 383 
alveolar walls. The fibers in the alveolar wall do not always 
run on the same side, but sometimes pass through the inter- 
capillary spaces and appear_in the opposite side of the wall. 
(In the mole, bat, and rat the fibers might also pass through the 
intercapillary spaces, but this could not be confirmed because 
of the insufficiently impregnated specimens.) The finest reticular 
fibers in the alveolar walls are so fine that the oil immersion is 
necessary. 
Lepus (rabbit). The situation here is similar to that in the 
guinea-pig, except that the fiber rings are coarser and the fiber 
nets in the alveolar nets are closer (fig. 34). 
Felis (cat) and Canis (dog). The nets of reticular fibers are 
in general very dense and the fiber rings of the mouths of the 
alveolar ducts and alveoli are exceedingly thick (fig. 35). The 
arrangement of the fibers is the same as in the above-described 
animals. The specimens obtained showed the fibers in relation 
to the capillaries very clearly. The reticular fibers in the alveolar 
walls pass over the capillaries superficially, but may sink slightly 
into the alveolar spaces. The thick fibers either pass over the 
capillaries unchanged or form then several fine fibers; this will 
be described under the reticular fibers in man. The fibers in 
the intercapillary spaces sometimes run very close along the 
contour of the capillaries, in which case they sometimes form 
closed rings, and sometimes they are slightly apart from the 
capillary and pursue a course parallel to them (fig. 36). This 
condition is probably the same in the guinea-pig and rabbit, 
although I was unable to show it. 
Homo (man). ‘There is no significant difference in fibers be- 
tween man and the cat or dog (fig. 37). Russakoff, however, 
points out that the reticular fibers of the alveolar walls of the 
human lungs seldom pass over the blood-capillaries. Contrary 
Fig. 33 Reticular fibers. The lung of the rat. Bielschowsky’s staining. 
x 150. 
Fig. 34 Reticular fibers. The lung of the rabbit. Bielschowsky’s staining. 
* 150. : 
Fig. 35 Reticular fibers. The lung of the deg. Bielschowsky’s staining. 
x 150. 
