The Baermann funnel technique is now well known to nematologists, but the modification here described was devised to facilitate the collection of large numbers of nematodes in a small volume of water with the minimum of plant debris present. The method has proved very satisfactory in obtaining nematodes for toxicity tests, for example, from “tulip-rooted” oats infested with stem eelworm. It is often a lengthy procedure to remove nematodes from a relatively large bulk of water such as is contained in a full watch-glass, particularly if much fine plant debris is also present. By means of the modification described an almost “pure culture” of nematodes is obtained, the amount of water being very little greater in volume than the nematodes.The apparatus is shown diagrammatically in Fig. 1:—The funnel, f, has resting in it a small metal sieve, s, which may easily be made by cutting off a section about ¾-in. deep from a piece of copper pipe of from 2½–8-in. diameter. Fine copper wire mesh, wm, is then soldered on to the bottom rim. This wire mesh need not be fine enough to retain all fragments of plant material, since a circle of fine bolting silk, bs, is laid within the sieve on top of the wire mesh, so that it fits exactly within the inside of the sieve. No bolting silk has yet been found which will retain living nematodes. The bolting silk, however, retains all plant material and is easily removed and cleaned.
Inclination of Baermann funnel wall and efficiency of nematode extraction.
