Procaine perfused into cerebral ventricles and subarachnoid space in conscious and anaesthetized dogs.

1. Perfusion of 1% procaine into the cerebral ventricles of conscious dogs produced mild paresis, defaecation, vomiting, jerky movements of eyelids, brisk nystagmus, increase in amplitude of respiration and sometimes loss of consciousness. Procaine 2% produced paralysis, loss of consciousness and sometimes respiratory depression.2. Procaine 2% perfused into the cerebral ventricles of dogs under chloralose anaesthesia produced an initial increase in amplitude of respiration, which preceded its final depression, which is due primarily to procaine and only partly to a change in pH.3. The site of action for the initial increase in amplitude of respiration was in the fourth ventricle, for it did not occur on perfusion of procaine into the cranial subarachnoid space.4. Perfusion of spinal subarachnoid space with procaine is enough to cause respiratory failure even when the procaine does not reach the medulla.