The Efficiency of the Baermann Apparatus in the Recovery of Larvae of Haemonchus contortus

Abstract

The apparatus commonly used for the isolation of nematode larvae from soil was first described by Baermann in 1917. It consisted of a glass funnel closed at the bottom by a clamp placed on a piece of rubber tubing attached to the shank, and a sieve of 1 mm mesh wire covered with a piece of coarse cloth. In order to isolate hookworm larvae from fecal cultures or contaminated soil, the funnel was filled nearly to the brim with filtered and sterilized water and the cloth covered screen containing soil or feces with hookworm larvae was placed in the water in the funnel. Samples of varying sizes were withdrawn from the bottom of the funnel at different intervals and examined for larvae. The temperature of the water was not stated. Cort, Ackert, Augustine and Payne (1922) tested the effect of various changes in the operation of the apparatus upon the recovery of hookworm larvae from soil. They found that the water must be at least 10? F warmer than the soil, that a higher percentage of larvae can be isolated from coarse than from finely divided soils, that a slightly higher percentage of larvae can be isolated from moist than from saturated soil, and that while most of the larvae escape from the soil into the water in the first 6 hours, an appreciable number come out later. They also found that under favorable conditions the percentage of larvae recovered was high but variable, the average being about 52 per cent. Stoll (1923) added known numbers of hookworm larvae to 100 gm samples of different types of soil, and used the Baermann apparatus under the conditions standardized by Cort et al (1922) to recover the larvae. He found that about 90 to 95 per cent of the larvae were recovered from humus, consisting mainly of vegetation in various stages of decay, about 80 per cent from sand and loam, and about 33 to 50 per cent from clay. Cort, Stoll, and Grant (1926) used water routinely at 45? C, after having found that of 1900-3750 mixed Ancylostoma and Necator larvae placed on 200 gram lots of moist clay-loam soil, and allowed to remain there