762 E, A. MINCHIN. 
corrected for coverslips, naked smears without coverslips do 
not give optical results so good as those covered, and that in 
covered smears it is optically preferable for the smear to be 
on the coverslip rather than on the slide. 
The majority of the preparations described here were done 
by Schaudinn’s method of making smears on a coverslip and 
then dropping the coverslip flat down plump into the fixative. 
T hold a coverslip in the fingers of my left hand, a glass rod 
in my right; in front of me is the liquid to be used for 
fixation. An assistant draws the drop of blood from a rat’s 
tail, and either places it on the coverslip I am holding, or I 
take it up on the end of the glass rod from the tail; in either 
case I smear the blood out with the glass rod and drop the 
coverslip, with the smear downwards, into the fixative. The 
whole process is done with one turn of the right wrist and one 
of the left, far more rapidly than a slide can be manipulated 
and with much less chance of drying or time for evaporation 
to take place. Coverslip smears made in this way are always 
stained and mounted in Canada-balsam without being allowed 
to dry during any part of the process. They are most con- 
veniently handled in solid watch-glasses (that is to say, a 
square slab of plate glass, two and a half inches square anda 
quarter of an inch in thickness, hollowed out on one side into 
a cavity the size of a watch-glass); the coverslip can be 
placed in this with only sufficient liquid to keep it wet on the 
underside (the side of the smear), and can be examined under 
the microscope with moderate magnification at any time, and 
the glasses can be stacked one on the top of the other to 
prevent the contents drying up. 
The use of coverslip smears necessitates a modification in 
the mode of applying the osmic acid vapour for fixation of 
films. I take a square block of hard paraffin of suitable size, 
and a glass ring ground flat on the two sides. The glass ring 
is gently heated and so cemented to the middle of one surface 
of the block of paraffin, which is then hollowed out into a small 
cell inside the glass ring. The osmic acid is placed in the 
cell in the paraffin, and the coverslip, with the blood-smear 
