371 
Every corpuscle thus becomes “set,” as it were, in its living 
form; there is no coagulation, no shrinking, no dissolution ; 
but, as the corpuscle was at the moment of exposure to the 
vapour, so it remains. The white corpuscles even exhibit 
their pseudopodial processes arrested in the act of movement. 
It is as though the osmic acid bottle contained a Gorgon’s 
head, which freezes the corpuscles, as they face it, into stone. 
Having been thus acted on by the osmic acid, the cover glass, 
with the blood on it, is placed on an ordinary glass slide, 
on which is a drop of a nearly saturated solution of acetate of 
potash, as recently recommended by Max Schultz (see the 
last number of this Journal), and there it may remain un- 
changed for as long as the physician wishes. The whole 
process is so simple that, in less time than it takes to examine 
the chest, a drop of blood may be taken, thus prepared, and 
placed on one side, for examination at a later moment. One 
may have perfect confidence, from careful comparative obser- 
vations (see below), that the osmic acid does not change the 
form of the corpuscles a¢ all, and thus all the advantages are 
obtained for a leisurely and deliberate study, which otherwise 
are only to be obtained by most inconvenient haste and pre- 
cipitation. At the same time the indispensable opportunity 
is provided of retaining the corpuscles in their living form 
for comparison from day to day and from case to case. 
6. The effect of pressure on the red blood-corpuscle of the 
frog and of man.—In fig. 3 a, a, corpuscles of the frog are 
drawn which were subjected to an oblique pressure, caused 
by squeezing the covering-giass under which they lay. A 
wrinkling of the surface has been produced, indicating the 
existence of a differentiated pellicle forming the outer wall. 
Such a wrinkling could not be produced were the corpuscle 
of homogeneous consistency. 
The same result, due to pressure, is observabl ein the 
human corpuscles drawn in fig. 18 f. 
In connection with the effect of pressure, I may refer to 
the observations which have been made by various microscop- 
ists on the tearing or cutting of the red corpuscle of the frog. 
It has been found that, by drawing a needle sharply across 
the slide on which a drop of blood is placed, the red cor- 
puscles may be cut or torn in halves, and that, under these 
circumstances, no escape of the viscid matter from the cor- 
puscle takes place, as would be expected were they membra- 
nous sacs containing a semi-fluid substance, but that the cut 
edges collapse, and each piece retains a rounded form. “This, 
though negativing the view that the corpuscles possess a 
membrane sharply limited on both sides, is not in antagonism 
VOL. XI,—NEW SER. BB 
