[Features of the respiration of the rat at a given tidal volume]

Intact rats were trained to breathe in a given tidal volume equal to VT; 0.8 VT; 0.6 VT; 0.4 VT. To decrease their spontaneous tidal volume rats were automatically punished with electric current for exceeding the given volume. All rats could breathe in the ranges VT and 0.8 VT maintaining the obligatory level of lung ventilation. It was difficult for them to breathe in the ranges 0.6 VT and 0.4 VT. In these cases the lung ventilation was lower than the obligatory one and the breathing was interrupted with hyperpnoea. Rats respiratory reactions depend on the range of the restriction. Three types of respiratory responses to the tidal volume restriction were found. The ability of rats to breathe in given ranges of the restriction are discussed.