1 6
A. MACFADYEN
The precise type of apparatus used depends on’ the completeness of extraction required, the medium to be investigated, the sources of heat
available and the groups of animals being investigated. Naturally,
large funnels are required for the larger, less numerous animals and if
only general collection is the aim, very simple apparatus such as collapsible funnels made of paper or polythene, suspended in the sunlight
will yield numerous animals. For more quantitative yields of larger
species, the rate of heating and humidity status in the funnel beneath
the sample become important. I n the case of compact humid soils of
temperate regions sufficient moisture can be derived from the soil itself
and humidity can be controlled by regulating the draught through the
funnel (Macfadyen, 196 1 ).
In work on micro-arthropods (mites and Collembola) sample-units of
about 25 cm2 area will usually yield high enough numbers for complete
counts and 10 cm2 for community studies. If counts are not to be biased
in favour of certain groups (as certainly happens in the normal Tullgren
funnel operated in dry conditions) it is necessary to arrange that humidity beneath the soil is high and the temperature low. These aims can be
achieved in the canister type extractor (Macfadyen, 1961), by standing
the canisters, into which the animals fall, in a water bath through which
cold water is circulated. Less accurate work, on the other hand, with less
elaboration, can be done with simpler extractors of the kind described
by Macfadyen (1953) and Auerbach and Crossley (1960). Frequently the
medium to be sampled will not permit the digging of cylindrical plugs
of soil such as are required for the above, because of the presence of
sticks in litter and of stones in soil. I n iihis case the canister extractor
cannot be used because the samples allow too much drying from above
and positive steps must be taken to ensure humid conditions beneath
the sample. This calls for an air conditioning system such as is incorporated in the 100 cm2 funnel extractor of Macfadyen (2961), an expedient which can only be realized in a properly equipped laboratory.
This extractor, which can, of course, also be used for soil sampling requires careful insulation if it is to be operated in a heated room and a
supply of cooling water (or a, refrigerator) which can extract about
2 cal of heat per minute. The simplest form of constriiction seems to be
a slotted angle steel frame with hardboard outer shell and insulating
panels of expanded polystyrene (“Jablite”) placed between the frame.
Full details are given in the above reference.
There is a growing tendency towards carefully planned community
studies in rather inaccessible places and consequently there is an urgent
need for an apparatus with which fairly complete extractions can be
achieved without the aid of electric current. I n an effort to meet this
need two extractors have been made recently, the first using paraffin
A. MACFADYEN
The precise type of apparatus used depends on’ the completeness of extraction required, the medium to be investigated, the sources of heat
available and the groups of animals being investigated. Naturally,
large funnels are required for the larger, less numerous animals and if
only general collection is the aim, very simple apparatus such as collapsible funnels made of paper or polythene, suspended in the sunlight
will yield numerous animals. For more quantitative yields of larger
species, the rate of heating and humidity status in the funnel beneath
the sample become important. I n the case of compact humid soils of
temperate regions sufficient moisture can be derived from the soil itself
and humidity can be controlled by regulating the draught through the
funnel (Macfadyen, 196 1 ).
In work on micro-arthropods (mites and Collembola) sample-units of
about 25 cm2 area will usually yield high enough numbers for complete
counts and 10 cm2 for community studies. If counts are not to be biased
in favour of certain groups (as certainly happens in the normal Tullgren
funnel operated in dry conditions) it is necessary to arrange that humidity beneath the soil is high and the temperature low. These aims can be
achieved in the canister type extractor (Macfadyen, 1961), by standing
the canisters, into which the animals fall, in a water bath through which
cold water is circulated. Less accurate work, on the other hand, with less
elaboration, can be done with simpler extractors of the kind described
by Macfadyen (1953) and Auerbach and Crossley (1960). Frequently the
medium to be sampled will not permit the digging of cylindrical plugs
of soil such as are required for the above, because of the presence of
sticks in litter and of stones in soil. I n iihis case the canister extractor
cannot be used because the samples allow too much drying from above
and positive steps must be taken to ensure humid conditions beneath
the sample. This calls for an air conditioning system such as is incorporated in the 100 cm2 funnel extractor of Macfadyen (2961), an expedient which can only be realized in a properly equipped laboratory.
This extractor, which can, of course, also be used for soil sampling requires careful insulation if it is to be operated in a heated room and a
supply of cooling water (or a, refrigerator) which can extract about
2 cal of heat per minute. The simplest form of constriiction seems to be
a slotted angle steel frame with hardboard outer shell and insulating
panels of expanded polystyrene (“Jablite”) placed between the frame.
Full details are given in the above reference.
There is a growing tendency towards carefully planned community
studies in rather inaccessible places and consequently there is an urgent
need for an apparatus with which fairly complete extractions can be
achieved without the aid of electric current. I n an effort to meet this
need two extractors have been made recently, the first using paraffin