1895] Microscopy. 197 
the disk of pith is embedded, so as to make it nearly transparent and 
so as to show the. shape of the adherent organisms through the semi- 
transparent block under a low power of the microscope. The proper 
cutting planes may now be marked or indicated on the margin of the 
block with lithographic ink or with a fine camel’s-hair pencil with lamp- 
black and turpentine. If the latter method is resorted to, great care 
must be exercised in scraping or shaving down the block to keep the 
plane along which the paraffine is removed parallel to the surface of 
the disk e. 
I have found it very easy to thus capture, hold, kill, dehydrate, stain, 
embed and cut Paramecium aurelia. Euplotes, Stylonychia and Hal- 
teria will also adhere to these disks. Halteria is about the size of a 
white blood-corpuscle, and the fact that it may be entrapped and 
treated as here described shows what a wide range of utility is promised 
by this new method of capturing and embedding minute organisms. It 
will doubtless also be found useful in the study of very minute eggs 
and larvee. 
I find that these pith disks, loaded with their adherent organisms, 
may be mounted entire, and one in this way may get most instructive 
preparations, often with half a dozen genera on a single slide. Stain- 
ing is also entirely under control, and any of the usual stains or ani- 
lines or combinations of them may be successfully applied and the 
action watched under the microscope and arrested at just the proper 
moment. With this method it has been found possible to cut 18 lon- 
gitudinal serial sections and 50 transverse serial sections of Parame- ` 
cium with a thickness of 2.5 to 5 » with the Ryder Microtome set to 1 
or 2 teeth of the micrometer wheel. ` 
The fixation of the sections on the slide may be effected by means of 
Gustav Mann’s albumen method. Take the white of an egg (30 c. c.), 
shake up with 300 c. c. of water for 5 minutes; filter twice. Paint 
clean slides on one side with this mixture with the aid of a glass rod, and 
stand up on end to drain and dry; 200 or more slides may be thus 
prepared and dried ready for use. The albumenized side of the dry 
sides may be distinguished by breathing upon them. The sections are 
to be stretched by floating the ribbon of paraffin containing them on 
warm water (30°c.). Immerse one end of the albumenized slide in 
the water and float and arrange the sections on it albumenized side 
uppermost. Place slide on water bath to dry, when the paraffin may 
be removed with xylol or turpentine after which the staining may be 
done on the slide. This method of fixing sections to slide with albumen 
is much simpler and more practical than with Meyer’s formula. 
