406 Collection and Preservation of Parasitic Worms 
Formalin should not, as a rule, be used for preserving nematodes if its use can 
be avoided. It is frequently the cause of serious damage to the specimens by 
bursting or collapse, either at once or when they are subsequently transferred 
to other fluids prior to examination. Sometimes, however, alcohol is not 
available, and in such cases a possible method is to kill the worms in hot water 
(about 70° C.), and then transfer to 3 per cent, formalin. As has been 
mentioned, heat is necessary for the best results, but, in the writer’s opinion, 
if alcohol is available but heating impossible, it is better simply to place the 
worms in cold 70 per cent, alcohol than to use formalin 1 . 
In cases where it is desired to preserve the histological details of nematodes 
for minute study, Prof. H. B. Ward recommends killing the worms in a mixture 
of equal parts of (1) acetic acid; (2) absolute alcohol; and (3) saturated watery 
solution of corrosive sublimate with 0*25 per cent, osmic acid. 
Acanthocephala. 
These worms swell up if left long in salt solution or water. They may be 
cleaned rapidly in the washing solution with a small brush, and then subjected 
to gentle pressure between two slips of glass until the proboscis is protruded. 
They may then be killed by running in strong alcohol between the slips, an 
even pressure being maintained (Braun and Liihe, Handbook of Practical 
Parasitology). After killing, they should be stored in 70 per cent, to 90 per cent, 
alcohol. 
Acanthocephala can also be treated by the hot alcohol method employed 
for nematodes, but it is important to fix them with the proboscis extruded if 
possible. 
When Acanthocephala are to be stained for examination (this is not always 
necessary for identification), Van Cleave recommends fixation in saturated 
corrosive sublimate solution, with 1 per cent, acetic acid, for about 15 minutes. 
The worms are then washed in water, and brought through 35 and 50 per cent, 
alcohol to 70 per cent, alcohol, and stored in the last. 
Trematodes. 
The following simple procedure gives satisfactory results for general pur¬ 
poses. After the preliminary shaking-up in salt solution, the dirty liquid is 
poured off, and a small quantity of fresh salt solution introduced. The worms 
are again shaken vigorously, and an equal volume of saturated corrosive 
sublimate solution (with, preferably, a few drops of acetic acid) quickly added. 
The shaking is then continued for a few minutes. The vigorous shaking not 
only cleans the specimens, but prevents muscular contraction, and so causes 
1 In certain special cases, such as Mermithidae and many of the Filariidae, formalin seems 
to give better results than alcohol. After very rapid cleaning, these worms may be killed in a 
5 per cent, solution of formalin. They may either be kept in this, or transferred to 70 per cent, 
alcohol by very gradual stages through 30 and 50 per cent, alcohol. It is better not to wash 
them in water after formalin. 
