776 
Journal o f Agricultural Research 
Vol. XXX, No. 8 
The disadvantages of this method of 
screening are mostly theoretical and 
generally follow errors of judgment. 
In the first place, it was found that in 
practice time could not always be 
saved by substituting the screening 
method for the sedimentation method. 
These cases were usually those in which 
washing itself was unnecessary. Such 
cases include the examination of the 
practically empty stomach of a fasted 
dog or the almost empty cecum of indi¬ 
vidual carnivores of any sort. In these 
cases the organs in question could be 
slit open into a jar, the material allowed 
to settle for a few minutes, the super¬ 
natant fluid decanted, and the small 
sediment examined immediately, or 
after one washing, in a glass dish. 
This is a quicker procedure than 
screening and examining the screens, 
and there is little in the way of ingesta 
or fecal material to conceal parasites 
or afford unpleasant odors. 
Another objection is on the score of 
possible injury to parasites by screen¬ 
ing and washing. For the practical 
purposes of routine examination for 
and collection of parasites, this objec¬ 
tion is mostly theoretical, although in 
special cases it would be sound. In 
general, worm parasites are fairly re¬ 
sistant structures as met with in the 
field of human and veterinaiy medi¬ 
cine. Such worms as the ascarids are 
fairly tough structures, and Ascaris 
lumbricoides has been kept alive in 
Kronecker’s solution for 26 days, which 
shows that it is not readily damaged by 
being removed from its host and placed 
in an alien environment. It is true 
that there are some very fragile worms 
that are very susceptible to mechan¬ 
ical injury and the destructive action of 
osmosis in such fluids as tap water, but 
worm parasites of the digestive tract 
are rarely of this sort. It is also true 
that the easily lost hooks of some tape¬ 
worms may be lost by screening. 
Where worms are being collected for 
very careful studies of their morphology 
a more refined technic is desirable; but 
for practical routine purposes the 
writers find the screening method supe¬ 
rior to the sedimentation and washing 
process, provided one uses good judg¬ 
ment, and believe that the contents of 
the small and large intestines may be 
screened to advantage in almost all 
cases and that screening of the contents 
of the stomach and cecum should be 
carried out when of sufficient quantity 
to warrant it or omitted if of such small 
quantity that little or no washing is 
necessary. The screening method would 
be of value for the examination of swine 
viscera and to some extent for the exam¬ 
ination of the viscera of such animals as 
sheep, cattle, and horses. 
In connection with the subject of 
laboratory technic it is also noted that 
it is advisable to slit the larger air 
passages of the lungs and then wash 
and squeeze the lung in a dish of water 
or saline solution in order to detect 
worms which may be overlooked in 
slitting and examining without this 
washing. The urinary bladder, gall 
bladder, and similar structures also 
should be slit in a dish of water or 
saline solution and examined in the 
same way and for the same reason. 
CONCLUSIONS 
A set of metal screens of assorted 
mesh apertures with a suitable rack 
to hold them is a very valuable and 
almost indispensable part of the equip¬ 
ment of a parasitological laboratory. 
The screens are of service in examining 
feces for parasite eggs and for worms 
passed after anthelmintic treatment 
and in examining the contents of the 
digestive tract post-mortem. If used 
with judgment in post-mortem exam¬ 
inations they save time, make the de¬ 
tection and collection of parasites easier 
and more certain, and make the work 
less unpleasant by removing the mal¬ 
odorous portions of ingesta and fecal 
material more rapidly than the sedi¬ 
mentation and washing method does. 
There appears to be little damage done 
to parasites, as a rule, by the use of 
screens and washing. The lungs, uri¬ 
nary bladder, gall bladder, etc., should 
be slit open in a dish of water or saline 
solution and examined in this way for 
parasites present. 
