774 
Journ al of Agricultural Research 
Vol. XXX, No. 8 
In their experiments, the writers 
have substituted the use of screens 
for the sedimentation and washing 
method in examining the digestive 
tract in all cases where such a sub¬ 
stitution saved time. The screens used 
were the same ones used by Hall 
and by Hall and Foster. These 
screens were made by taking round tin 
pans with a bottom diameter of about 
6.5 inches and a slightly greater top 
diameter, with sides 2 inches high, 
and with a projecting flange rim at the 
top, cutting out most of the bottom of 
the pan, but leaving a small flange 
projecting inward, and soldering brass 
screening of assorted sizes to the bottom 
flanges of the various pans. Some of 
the pans were enameled and some 
shellacked to prevent rusting. The 
enamel and shellac have never been 
renewed since the first coat, and these 
screens—very cheap affairs to begin 
with—are still serviceable after about 
14 years of constant use. The ex¬ 
pense of screens is therefore a very 
small matter, and even poorly equipped 
laboratories can easily afford them. 
A much better set of screens for the 
purpose has been described by Hall. 6 
These screens (fig. 1) are of copper and 
are about 7% inches (20 cm.) square 
in inside dimensions. They are made 
of two copper strips, swaged together 
at two diagonal corners, the top half¬ 
inch of the metal being bent over and 
doubled back against the side on two 
opposite sides to form a reinforced 
flange 34-inch wide which carries the 
screen in a rack. The copper sides 
are 2 inches high. On the bottom of 
the screens the metal is bent in to 
form a flange z /% inch wide for the 
attachment of the brass screening, 
which is soldered to this flange. The 
screens described had mesh apertures 
of 6, 8, 10, 14, 16, 20, 60, 100, and 120 
to the inch, the latter being about the 
finest screen that will permit of the 
passage of the eggs of practically 
any worm parasite. Each sieve has a 
number stamped in the front side 
to show its number of mesh apertures 
to the inch. A solid-bottomed copper 
pan, of the same shape and dimensions 
as the screens, completes the set. A 
rack with grooves in its solid board 
sides or with transverse pieces on the 
sides and back of a skeleton construc¬ 
tion of upright pieces is provided, and 
the screens are supported by the 
grooves or transverse pieces when they 
are set up in the rack. The number 
of screens used in any operation will 
vary with the nature of the material 
examined and the judgment of the 
operator. 
The material which the writers have 
examined post mortem by means of 
screens consisted mostly of the con¬ 
tents of digestive tracts of dogs killed 
at the end of experiments in critical 
testing of anthelmintics, and of diges¬ 
tive tracts of wolves, coyotes, lynxes, 
and one bear sent in by the field service 
of the Biological Survey of the Depart¬ 
ment of Agriculture in response to a 
request by the Zoological Division for 
this material. The viscera of the dogs 
were fresh. The viscera of the wild 
carnivores were sent from the field 
wrapped in borax or in cloth saturated 
in formaldehyde solution, some of 
them coming from as far as California, 
and were often a week or ten days old 
when received. 
THE SCREENING METHOD 
The method of screening the con¬ 
tents of practically all portions of the 
digestive tract, including the stomach, 
small intestine, cecum, and large in¬ 
testine, was first tested, each of these 
portions being opened separately into 
a jar of water and each screened 
separately. For this purpose the three 
screens having 6, 12, and 24 mesh 
apertures to the inch were generally 
used. The finest of these screens 
shows some little variation in its mesh 
apertures and may have in places 21 
or 22 mesh apertures to the inch. It 
is not so fine as could be desired for 
the final screen, and the 60-mesh screen 
was sometimes used as a final screen. 
One with a mesh aperture of perhaps 
40 to the inch should probably be 
added to the set. The number of 
screens and the mesh sizes to use are 
matters of individual judgment. The 
screens should be used in a rack for 
various reasons, one reason being that 
this results in cutting down the water 
pressure on the last screen and dimin¬ 
ishing the likelihood of washing worms 
through that screen by high-water 
pressure. 
The advantages of this method over 
the sedimentation and washing method 
are very evident. As soon as the con¬ 
tents of a jar are poured on the screen, 
a hose which is attached to a water 
tap having a foot-pedal control for the 
flow is used to wash the material on 
the top screen until it is clean and 
comminuted as much as possible. 
The pressure of the water and the 
amount of washing are matters of 
individual judgment. The water runs 
6 Hall, M. C. apparatus for use in examining feces for evidences of parasitism. Jour. Lab. 
and Clin. Med. 2: 347-353, illus. 1917. 
