1. Breath-holding test was applied both under ordinary and under-water conditions to the same subjects, and the breath-holding time, CO
1 content and O
2 content of the alveolar air were determined in each subject
2. For collecting the sample of the alveolar air, a modified collecting tube was designed, making it more suitable for a field work.
3. In primary school children, the breath-holding time increases with the age both under ordinary and under-water conditions. The longer breath-holding time is accompanied with increased CO
2 content of the alveolar air after the test.
4. Generally speaking, breath can be held longer under ordinary conditions than under the water. Here also the longer breath-holding is accompanied with greater CO
2 content of the alveolar air after the test.
5. The age difference in the breath-holding time may be due to the sensitivity and/or the volitional effort of endurance.
6. For the shorter endurance in the. under-water breath-holding, not only psychological, but also technical factors on the part of the tested subject may be responsible.
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