350 CHIKANOSUKE OGAWA 
In the lungs of these two mammals, just as in birds, no impreg- 
nation of cement line occurs with the ordinary silver method, 
but it can be brought about by using concentrated solutions, 
or osmium-silver. I examined these cement lines in various 
ways and it became clear that the lines belong to the endothelium 
of the blood-eapillaries for the following reasons: 
1. Following the blood-capillaries to the blood-vessels, I was 
able to show that the cement lines on the blood-capillaries are 
sometimes continuous with those of the blood-vessels. 
2. As already mentioned, the intercapillary spaces are pores, 
but in the places where they come into contact with other tissue, 
such as pleura, they cannot form any pores. If the cement 
lines, which appear on the blood-capillaries by the silver method, 
belong to the respiratory epithelium, they ought to continue to 
the spaces at this place. In order to decide this question I cut 
the silver preparations tangentially to the surface of the pleura 
and found that under the microscope some of the intereapillary 
spaces in the bases of the alveoli, which adjoined the pleura, 
contained one or two round, nucleated cells, while in other 
similar spaces there was no coating of cells at all. This can 
also be seen in stained section. Even with the most careful 
examination I could not follow the cement lines of the blood- 
capillaries to the spaces. 
From this it must be concluded that by injection of the air 
passages with silver solution, capillary endothelial cells are the 
only ones which are impregnated, except for the cells at the bases 
of the alveoli adjacent to pleura, which are also impregnated. 
The embryos collected for the study of development of respira- 
tory epithelium in the mole were of too earlier stages, but in the 
young mole I perceived frequently round nucleated cells in the 
intercapillary spaces, but no trace of epithelial cells on the 
blood-capillaries. 
From these studies it seems most probable to conclude that in the 
mole and bat, as in the bird, there is no coating of respiratory epi- 
thelium. 
B. Respiratory epithelium in adult mammals. It is generally 
believed at present that the respiratory epithelium of adult 
