194 The American Naturalist. [February, 
MICROSCOPY.’ 
On a New Method of Entrapping, Killing, Embedding 
and Orienting Infusoria and other very small Objects for 
the Microtome.—aA reliable method for capturing, killing, staining 
and dehydrating minute organisms has long been a desideratum with 
biologists, especially when such objects fall far below 1-100th of an 
inch or 1-40th mm. in diameter. After trying a number of devices, 
all of which failed, I fortunately hit upon a plan that is not only very 
simple, but also capable of wide application, since I find that by its 
means organisms as small as 1-2000th inch or 12.5» in diameter 
may be caught and held. 
With the ordinary methods of filtration through the filter paper it 
is not possible to afterwards separate minute organisms thus captured 
from the surface of the substratum of paper. This difficulty has been 
overcome in my new method by means of a filter that can be easily cut 
in the block along with the objects adherent to its surface and within 
its meshes, a procedure quite impossible with filter paper. While fil- 
tration is the basis of this new method, and the use of ordinary filter 
paper is an essentially important part of it, it has been found necessary 
to find a substance that would serve as a filtering membrane that was 
porous, but not fibrous, because the presence of fibres is fatal to any 
attempt at cutting good sections in paraffine. On such a filtering 
membrane the organisms are caught and held where they are killed or 
fixed with any reagent, stained, dehydrated, and embedded, filter and 
all, in paraffine by means of the watch-glass method. 
The filter upon which the objects are caught and killed consists of 
thin slices of elder pith. Get good, clean, whole pieces of elder pith, 
and clamp a piece of it into the holder of a Schanze or other sledge 
microtome, so as to make transverse sections of it, taking about four 
to six divisions of the micrometer wheel to each section. The micro- 
tome knife should be set at an acute angle with the line of movement 
of the knife carriage, as in cutting celloidin. With fresh pith, some- 
what thinner sections may be cut. Upon examining such discoidal 
slices of elder pith, they will be found to be perforated at pretty regu- 
lar intervals by openings caused by cutting through the very thin cel- 
lulose walls of certain of the pith cells. The pith filter is, it is thus 
seen, mechanically produced by the help of the microtome. A good 
‘Edited by C. O. Whitman, University of Chicago. 
