362 CHIKANOSUKE OGAWA 
flattened even in the presence of nuclei. This is clearly shown in 
figure 13, which represents the preparations made from an 11- 
em. rabbit embryo, expanded by silver solution. It can be seen 
in a view of sectioned alveolar walls that the nuclei are flattened 
in accordance with the flattening of the cells. 
According to Ebner and Schulze, the fusion of the epithelial 
cells is partly responsible for the formation of flat cells. But 
hitherto no positive proof of the fusion of embryonic epithelial 
cells has been given, and, as figure 13 shows, the flat cells can be 
formed without fusion, so that it seems superfluous to look for 
the cause there. 
In conclusion of this topic, a brief description of the blood- 
capillaries of the alveolar walls of embryonic lungs may be given. 
It is already known that in the foetal circulating system most of 
the blood from the right ventricle flows into the aorta and only 
a small amount of it enters the lung. Therefore I imagine at 
first that the blood-capillaries of the alveolar walls would be in a 
somewhat collapsed state. But, on the contrary, the micro- 
scopic examination shows that the capillaries are filled with 
blood-corpuscles. Therefore, it cannot be true that the collapsed 
blood-capillaries are extended and produce new lumina at the 
time of the first respiration, but they increase in their length 
and caliber only in accordance with the expansion of the alveoh, 
and in consequence of increase of capacity the blood starts to flow 
into the lung from the general circulation. 
E. Reparation of respiratory epithelium. There must be a 
limit to the duration of the respiratory epithelium. It would be 
an interesting problem to investigate how the degenerate epi- 
thelial cells, especially non-nucleated cells, are repaired, but up 
to this time there has been no report made along this line. 
There is a distinct difference between the small, nucleated 
cells and large, non-nucleated cells in ordinary microscopical 
preparations, and no intermediate forms are found. The proc- 
esses of reparation or regeneration cannot be followed in such 
material. In order to bring about regeneration in an experi- 
mental way, I tried several methods. At first I injected the 
various kinds of macerating solutions, such as alcohol, chromic 
