404. R. S. CUNNINGHAM 
cent alcohol, dehydrated, and embedded as rapidly as possible. 
Blocks were also fixed in 95 per cent alcohol, it having been found 
that the dye did not diffuse out to any appreciable extent from 
tissue fixed in strong alcohol. Sections were cut parallel to the 
surface and all the surface sections carefully preserved in series. 
In this way some slight shrinkage of the tissues occurred as 
determined by control preparations, but any loss of dye from 
the cells was reduced to a minimum. Finally, very thin mem- 
branes were obtained by stripping small bits of the surfaces of 
organs while the blocks of tissue were in 80 per cent alcohol; 
these were stained and cleared, and while many were entirely 
too thick for careful study, others were obtained which were 
as thin and easily analyzed as omental spreads. In general 
there seems to have been some loss even in these preparations, 
as could be determined by the control studies in fresh material, 
but the loss was in no way sufficient to prevent cellular orienta- 
tion, which is obviously the one difficulty in the interpretation 
of the cells removed by scraping. 
It is a pleasure to thank Mr. Didusch for the care and accu- 
racy with which he made the excellent drawings. 
EXPERIMENTAL RESULTS 
The cells which line the peritoneal cavity may be divided 
into four classes by means of the reactions to vital dyes. These 
are all closely related to each other, agreeing in certain partic- 
ulars which seem to be very fundamental, while they differ in 
minor points which are probably in some way related to the 
function of the organs which they cover. The classification 
into four groups is not to be considered as absolute, because 
variations in one may approach the normal in another, but the 
general types are sufficiently distinct to require separation. 
1. General serosal mesothelium, including the cells covering: 
. intestine. 
. body-wall. 
liver, pancreas, etc. 
. mesentery. 
. diaphragm. 
Be S57 Ss S 
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