SOME LABORATORY METHODS FOR PARASITOLOGICAL 
INVESTIGATIONS 1 
By Maurice C. Hall and Eloise B. Cram, Zoological Division , Bureau of 
Animal Industry , United States Department of Agriculture 
INTRODUCTION 
The post-mortem examination of 
the viscera of animals for parasites 
constitutes a large part of the work 
of a laboratory of parasitology, and 
the efficiency of the work depends 
largely on the effectiveness of the 
methods used in such examinations. 
Owing to the general prevalence of 
parasites in the digestive tract, the 
examination of this tract is of special 
importance. 
The method of examining the diges¬ 
tive tract which is most widely em¬ 
ployed in laboratories is substantially 
as follows: The esophagus is removed, 
slit with the indispensable enterotome, 
and examined by reflected light for 
evidence of parasites superficially vis¬ 
ible and by transmitted light for 
parasites embedded in the tissue and 
not superficially visible. The stomach 
is opened into a jar of water or physi¬ 
ologic saline solution, the contents 
washed out, the stomach itself ex¬ 
amined internally, externally, and if pos¬ 
sible by transmitted light for parasites 
present, and the stomach contents re¬ 
peatedly sedimented and washed until 
the supernatant water or saline solution 
is clear, the sedimented contents then 
being examined a bit at a time after 
being poured into wide, shallow glass 
dishes. The small intestine or its com¬ 
ponent portions, the cecum, and the 
large intestine or its component por¬ 
tions are examined in the same man¬ 
ner as the stomach. 
This method has long been in use 
and is, as a rule, a fairly satisfactory 
procedure. It is best suited for ex¬ 
amining the digestive tract of such 
animals as dogs. In the case of a larger 
animal, such as a horse, cow, or sheep, 
the contents of the stomach and large 
intestine are so bulky that this method 
of examining is unsatisfactory, and as 
a rule the examination is confined to 
the region of the mucosa and the con¬ 
tents near the mucosa, the interior of 
the mass of ingesta or fecal material 
receiving little or no attention in many 
cases. This was the method employed 
by Looss 2 in examining horses for 
parasites. In some cases the con¬ 
tents of the large intestine (cecum and 
colon) of the horse are examined by 
pressing the material into balls and 
picking these apart by hand. This was 
the method employed by Hall, Wilson, 
and Wigdor 3 and they used the same 
method for examining the manure of 
horses for worms passed after anthel¬ 
mintic treatment. 
THE USE OF SCREENS 
It has occurred to the writers that 
the use of the graduated set of screens 
which they find indispensable in 
examining feces for parasite eggs and 
for worms passed after anthelmintic 
treatment in the case of dogs and 
similar small animals, might be of 
value in post-mortem examination as 
well. Various other writers, such as 
Stiles, Cobb, '•Telemann, Bass, and 
Garrison, had advocated the use of a 
screen or sieve of metal, gauze, or 
bolting cloth in the examination of 
feces for parasite eggs; but the advan¬ 
tage of a set of metal screens of gradu¬ 
ated sizes, set in a rack in the order 
of size with the largest-mesh screen 
at the top and the smallest-mesh 
screen at the bottom, appears to have 
been emphasized first by Hall . 4 This 
set of screens was also used in ex¬ 
amining feces for worms passed after 
anthelmintic treatment in critical test¬ 
ing of anthelmintics by Hall and 
Foster . 5 The usefulness of assorted 
screens for the separation of mixtures 
of objects of various sizes is generally 
recognized in industrial procedures. 
Feces and gastro-intestinal contents 
are mixtures of this sort. 
1 Received for publication June 30, 1924; issued June, 1925. 
2 Looss, A. THE SCLEROSTOMIDAE OF HORSES AND DONKEYS IN EGYPT. Rec. Egyptian Govt. School 
Med. 1901: 25-138, illus. 1901. 
3 Hall, M. C., Wilson, R. H., and Wigdor, M. the anthelmintic treatment of equine intestinal 
strongylidosis. Jour. Amer. Vet. Med. Assoc, (n. s. 7) 54: 47-55. 1918. 
4 Hall, M. C. A comparative study of methods of examining feces for evidences of para¬ 
sitism. U. S. Dept. Agr., Bur. Anim. Indus. Bui. 135, 36 p., illus. 1911. 
« Hall, M. C., and Foster, W. D. efficacy of some anthelmintics. Jour. Agr. Research 12: 397, 
447, illus. 1918. 
Journal of Agricultural Research, 
Washington, D. C. 
( 773 ) 
Vol. XXX, No. 8. 
Apr. 15, 1925. 
Key No. A-96 
