Calculation of Intensity and Efficiency of Nutrition
119
filtrate. The sample is heated to 80°C, cooled, and the precipitate of BaC03 is
filtered on a Millipore filter, which is then placed into the scintillation vial for
radioassay with quench correction using an internal standard.
The radioactivity of feces (rf) is determined by counting the filter after
filtration of a water sample taken from the aquarium in which the labeled
animals have been exposed. The filter should be dissolved in the scintillation
vial with ethylene glycol and then radioassayed. The value of radioactivity
found per sample is calculated for the total volume of the aquarium or holding
vessel and then per individual animal. The dissolved or colloidal excretions
passing through the filter can be measured by combustion of evaporated
subsamples of the liquid after removing feces by filtration.
3.4.4 Estimation of the Inverse Specific Radioactivity of CO2
Respired by Labeled Animals (Cq)
The estimation of the Cq values is important to calculate the absolute quantity of assimilated organic carbon of labeled food lost in respiration as well as
to analyze the rate of entry of newly utilized food into the metabolism process.
This value can be estimated either directly or indirectly.
1. The direct method
The direct method to estimate Cq can be used only for larger animals having
a wet weight over 200 mg. An experimental vessel of 100-150 ml is filled with
water free of CO2 (boiled with HCl and subsequently cooled and the pH
adjusted to 8.3 with a KOH solution free of CO2; see Sect. 3.3.1). The labeled
animals (usually 20-40 individuals) are passed two times through water free
of CO2 and are then placed into the experimental vessel, which is closed after
removal of 10 ml water to leave a layer of air under the stopper. A parallel
blank vessel with the same water must also be prepared. After 1-2 h of exposure, the water is transferred into the flask, which is attached to the apparatus
(Fig. 2.3), and the CO2 evolved by the animals is distilled out after acidification
and boiling. The CO2 is absorbed in the absorber with 0.05N KOH. After
resuming distillation, this alkaline solution is washed out of the absorber into
a small flask of about 30ml volume to which a solution of BaCl2 is added. The
mixture is heated in a water bath at 80°C, cooled, and titrated with 0.025 N
Hel in the presence of phenolphthalein as indicator to a slight pink color. The
carbonate carbon is calculated taking into account the results of the blank
estimation: 1 ml of 0.025 N HCl corresponds to 150 Ilg C. After completing the
titration, the liquid is immediately made alkaline again with 1 ml 0.4 N KOH,
kept for 5 min at a temperature of 80°C, then cooled. The precipitate of BaC03
is filtered through a Millipore filter, which is then placed into the scintillation
vial. The filter is dissolved in it by addition of 1 ml of ethylene glycol the BaC03
precipitate is resuspended and radioassayed with 15 ml of Aquasol scintilla-
119
filtrate. The sample is heated to 80°C, cooled, and the precipitate of BaC03 is
filtered on a Millipore filter, which is then placed into the scintillation vial for
radioassay with quench correction using an internal standard.
The radioactivity of feces (rf) is determined by counting the filter after
filtration of a water sample taken from the aquarium in which the labeled
animals have been exposed. The filter should be dissolved in the scintillation
vial with ethylene glycol and then radioassayed. The value of radioactivity
found per sample is calculated for the total volume of the aquarium or holding
vessel and then per individual animal. The dissolved or colloidal excretions
passing through the filter can be measured by combustion of evaporated
subsamples of the liquid after removing feces by filtration.
3.4.4 Estimation of the Inverse Specific Radioactivity of CO2
Respired by Labeled Animals (Cq)
The estimation of the Cq values is important to calculate the absolute quantity of assimilated organic carbon of labeled food lost in respiration as well as
to analyze the rate of entry of newly utilized food into the metabolism process.
This value can be estimated either directly or indirectly.
1. The direct method
The direct method to estimate Cq can be used only for larger animals having
a wet weight over 200 mg. An experimental vessel of 100-150 ml is filled with
water free of CO2 (boiled with HCl and subsequently cooled and the pH
adjusted to 8.3 with a KOH solution free of CO2; see Sect. 3.3.1). The labeled
animals (usually 20-40 individuals) are passed two times through water free
of CO2 and are then placed into the experimental vessel, which is closed after
removal of 10 ml water to leave a layer of air under the stopper. A parallel
blank vessel with the same water must also be prepared. After 1-2 h of exposure, the water is transferred into the flask, which is attached to the apparatus
(Fig. 2.3), and the CO2 evolved by the animals is distilled out after acidification
and boiling. The CO2 is absorbed in the absorber with 0.05N KOH. After
resuming distillation, this alkaline solution is washed out of the absorber into
a small flask of about 30ml volume to which a solution of BaCl2 is added. The
mixture is heated in a water bath at 80°C, cooled, and titrated with 0.025 N
Hel in the presence of phenolphthalein as indicator to a slight pink color. The
carbonate carbon is calculated taking into account the results of the blank
estimation: 1 ml of 0.025 N HCl corresponds to 150 Ilg C. After completing the
titration, the liquid is immediately made alkaline again with 1 ml 0.4 N KOH,
kept for 5 min at a temperature of 80°C, then cooled. The precipitate of BaC03
is filtered through a Millipore filter, which is then placed into the scintillation
vial. The filter is dissolved in it by addition of 1 ml of ethylene glycol the BaC03
precipitate is resuspended and radioassayed with 15 ml of Aquasol scintilla-