404 Collection and Preservation of Parasitic Worms 
solution may induce the worms to loosen their hold. The same remarks apply 
to Acanthocephala, but these must sometimes be literally dissected out. 
In dealing with nematodes in capsules, cysts or tumours, or buried in 
tissue of any kind, it should be remembered that it is usually easier to remove 
and clean them in the fresh condition than after the surrounding tissue has 
been hardened with fixatives. Even when fresh, they are often very difficult to 
extract whole and undamaged. They should be dissected out as carefully as 
possible. Sometimes, if the enclosing tissue be cut out and placed for a short 
time in salt solution, the worms will emerge of their own accord. 
Washing. 
All intestinal worms should be washed, after collecting and before killing, 
to free them from adherent mucus and other matter. This, in most cases, 
is best accomplished by shaking up in a tube or jar of normal salt solution 1 
or tap-water. In the case of nematodes possessing a mouth-capsule, the shaking 
should be vigorous, in order to remove epithelium and other matter from the 
mouth. No damage will result to nematodes and trematodes from a fairly 
severe shaking, but with cestodes care must be exercised. The specimens, 
obtained by scraping or otherwise, should be gently shaken in a jar with plenty 
of fluid, or merely washed in a dish. When they are long and tend to become 
tangled, they should be kept as far apart as possible in a shallow dish, or rinsed 
separately and spread out on a glass plate with a minimum of fluid. For 
washing cestodes, Dr Meggitt recommends plain lukewarm water in preference 
to salt solution, unless it is important to preserve the cuticle in perfect con¬ 
dition. In this case cold salt solution should be used. 
Washing should in no case be too prolonged. In the case of small nematodes, 
immersion in a watery solution for more than a few minutes is apt to cause 
local or general swelling of the cuticle, and sometimes the specimens will burst. 
It is therefore desirable, as a rule, to kill the worms as soon as possible after 
they have been collected. In the case of certain elongated and active nematodes, 
such as the lung-worms of sheep and pigs, it is necessary to keep them apart 
as far as possible during the washing process, and to kill them quickly, in order 
to prevent them from becoming a tangled mass. 
Should it be desired to keep worms alive for a time, it is better, as a general 
rule, to leave them in their natural element than to remove them to water 
or salt solution. 
Fixation and Preservation. 
It is important to use methods of killing which will fix the tissues in a 
condition as nearly as possible resembling that of life, and leave the specimens 
in a suitable condition for subsequent microscopical examination, without 
1 A 1 per cent, solution of salt is sufficiently accurate for practical purposes. In the opinion of 
some authorities, tap-water is better for intestinal nematodes than salt solution or distilled water. 
For nematodes from the alimentary canal of fresh-water fishes, Prof. H. B. Ward recommends 
a 3 per cent, salt solution. 
