EUTHANASIA OF DAY-OLD CHICKS WITH CARBON-DIOXIDE AND ARGON

The efficacy for the euthanasia of day-old chicks of mixtures of carbo n dioxide and air, or carbon dioxide and argon containing 1, 2 or 5 pe r cent residual oxygen, or argon containing 1 or 2 per cent residual o xygen was tested in three experiments, The time to the onset of uncons ciousness of individual chicks, determined from the time to loss of po sture, was similar during their exposure to 2 per cent oxygen in argon , 20, 30 or 40 per cent carbon dioxide in argon with 2 per cent residu al oxygen, or 90 per cent carbon dioxide in air, The exposure of chick s in batches of 20 to a mixture of 20, 30 or 40 per cent carbon dioxid e in argon resulted in the death of all the chicks within two minutes, However, a residual oxygen level of 5 per cent in these mixtures resu lted in the survival of some chicks for longer than two minutes, With argon alone the level of residual oxygen was critical; less than 2 per cent was essential to achieve 100 per cent mortality within three min utes, and a rise from 2 to about 3 per cent resulted in up to 20 per c ent of the chicks surviving for seven minutes.