RESPIRATORY SPACES OF THE LUNGS 205 
It is very difficult to combine injection in the capillaries with 
silver impregnation. As already shown, the small nucleated 
cells are located in the intercapillary spaces and the non-nucleated 
cells in the intercapillary spaces and on the capillaries, which 
are common to two adjacent alveoli, 
An intercapillary space is generally coated on one side of the 
alveolus by a nucleated cell and on the other side by a non- 
nucleated cell; it seldom happens that an intereapillary space 
has nucleated cells on both sides of the alveolar wall. According 
to Kolliker, the small nucleated cells may be sometimes absent 
from the intereapillary spaces; but in my opinion this is a frequent 
occurrence, and such spaces are naturally lined by the non- 
nucleated cells. On the contrary, the small, nucleated cells are 
apparently only seldom situated on the blood-capillaries. 
It was first affirmed by Kolliker that the large cells had no 
nuclei. But in his investigation he used only the silver method, 
and in his conclusion he is less emphatic, saying only that they 
appear to have no nuclei. Since then his statement has been 
accepted without sufficient examination and it has been assumed 
that because the silver method did not reveal nuclei in the large 
cells, while it. did in the small, the former contained no nuclei. 
But, as previously described, the presence of the nuclei in large, 
flat cells of such reptiles as the tortoise and snake is never demon- 
strated by silver impregnation alone and can only be confirmed 
by the aid of other methods, so that the absence of nuclei in 
mammalian material had not been proved. With this in mind, 
I attempted by various methods to settle the question. There 
seem to be only three methods which are applicable to this 
purpose—the first, maceration of non-nucleated cells; the second, 
staining of nuclei by dye-stuffs in impregnated preparation, and 
the third, examination of silver impregnated material in a less 
refractive medium. The first method consists in injecting a 
macerating solution into the air passages in order to strip the 
epithelium from the subjacent layer and determining whether or 
not the isolated cells have nuclei, but the large, flat cells are 
easily damaged by macerating solution, as they are very delicate, 
so that this method is always a failure. The second method at 
