RESPIRATORY SPACES OF THE LUNGS 363 
acid, and so on, into the lung through the thoracic wall of the 
rabbit with a hypodermic syringe, and after various intervals 
of time I killed the animals and impregnated the lungs. But no 
impregnation of the injected areas was obtained because of the 
inflammation and exudation which occurred there, precluding 
impregnation. Injection of macerating fluids into the trachea 
was also unsuccessful. I then tried injecting the lungs of the 
rats with 0.5 ec. of distilled water through the trachea and exam- 
ined the impregnated lungs after various intervals of time. In 
some of the preparations areas were discovered in which no 
exudation had occurred and which showed certain variations in 
the respiratory epithelium. Besides the normal nucleated cells 
there occurred remarkably small and remarkably large nucleated 
cells, the latter being, in some cases, as large as the non-nucleated 
cells (fig. 18). Briefly, I discovered nucleated cells of various 
gradations of size. How can this best be explained? It seemed 
possible to interpret the small cells as the results of cell division, 
since they could not very well have become small as results of 
irritation due to injection of water, and often occurred in pairs. 
The presence of the nucleated cells which are larger than normal 
may be interpreted either as the results of swelling caused by 
slight irritation or as the result of change which the nucleated 
cells undergo in order to make up for the loss of non-nucleated 
cells. If the swelling be supposed to be the explanation, then 
the cells would have increased not only flat, but in all directions. 
I found, however, that the nucleated cells of various sizes seem 
to extend in one plane only, so that I am inclined to believe 
this increase in the size of the nucleated cells to be due to some- 
thing else than mere swelling from injection of water; and it 
seems quite probable that the nucleated cells are able to change 
into large, flat cells. I would then suggest the following sequence 
of events. As a consequence of water injection of the lung, a 
slight inflammation takes place which leads to desquamation of 
the epithelial cells, after which the small nucleated cells change 
into large, flat ones in order to make up for the loss of the epi- 
thelial cells, especially flat non-nucleated ones, and at the same 
