1. Deafferentation of the thoracic segments of the spinal cord causes a decrease in electrical activity of the abdominal muscles. A definite decrease in activity is observed after deafferentation of five segments. The increase in respiratory activity of the abdominal muscles which follows increased resistance to expiration is diminished or completely abolished after division of the dorsal roots. 2. Stretch receptors located in the abdominal muscles are found by recording dorsal root activity. Depending on the relationship between discharges of the receptors and phases of the respiratory cycle, “inspiratory,” and “expiratory” receptors and receptors the frequency of whose discharges is independent of the phases of respiration may be distinguished. Receptors working as “expiratory” are more numerous in decerebrate animals than in anesthetized animals. An increase in respiratory activity leads to an increase in frequency of discharge at expiration. This increased discharge is facilitated by the γ-system.