CELLS LINING THE PERITONEAL CAVITY 403 
the relationship which exists between the fibroblast and the 
serosal cell? Finally, a careful study of the way in which serosal 
lining cells react to vital dyes may throw some additional light 
on the interrelationships of different areas of mesothelium and 
on the physiology of these cells, both individually and as a living 
membrane. 
MATERIAL AND METHODS 
It is obvious at once to anyone who has studied the cells lining 
the peritoneal membrane that sections cut in the ordinary manner 
perpendicular to the flat surface of the cells could yield but little 
information as to the extent or arrangement of the dye concre- 
tions in the entire cell. It is, I think, this fact that has caused 
so many observers to conclude that the cells are entirely free 
from the dye; while most of those who have described the granu- 
lation have studied the cells in the omentum where they can be 
observed in their entirety by means of spread preparations. 
The observations reported here have been made from a series 
of experiments on rabbits. The animals were stained with 
Griibler’s trypan blue or with carmine prepared according to 
Kiyono’s method. Both dyes were usually administered in- 
travenously at intervals of twenty-four or forty-eight hours, the 
animals received from six to thirty doses of carmine, from three 
to twenty doses of trypan blue, and were usually sacrificed one 
to two days after the last injection. 
In the study of the cells several methods were used. The 
animal was anesthetized and the abdomen opened, cells were 
scraped from the surfaces of all the viscera, diaphragm, and 
body-wall, and were studied immediately. Smears were also 
prepared in a similar way, fixed by heat or alcohol and then stained 
in an appropriate manner to obtain good contrasts. Spread 
preparations of omentum and mesentery were studied fresh. 
Omental spreads were fixed by immersion for one hour in osmic 
acid or neutral formalin, washed quickly and stained; others 
were treated with weak (4 to 1 per cent) silver nitrate, ex- 
posed to sunlight, and then fixed in alcohol. Very thin blocks 
of all the organs which border the peritoneal cavity were fixed 
in neutral formalin for one hour, and then transferred to 80 per 
