Six years ago Dr. Shennan and I recorded the observations that rats which had been fed with cultures of a threading diphtheroid bacillus, isolated from the bronchus of a general paralytic, developed symptoms of paresis, which tended to go on to a fatal termination, and that the tissues of the animals showed changes resembling those that are found in cases of early general paralysis. In all of four animals in which the experiment was fully carried out the brain showed periarteritis, neuroglia proliferation and severe nerve-cell lesions. Two years ago Dr. McRae and I recorded some further experimental observations upon the effects of feeding rats with various strains of diphtheroid bacilli. A diphtheroid bacillus, which formed acid in glucose and saccharose test broths, and which was virulent to mice (Bacillus paralyticans brevis), produced very striking results in twelve animals. They developed acute or chronic forms of general paresis which went on to a fatal termination. The most marked lesions found after death were those affecting the nerve-cells of the spinal cord and brain, but in several of the animals there were also distinct periarteritis and neuroglia hypertrophy. Similar experiments with several other strains of diphtheroid bacilli, which could be classed as one or other of the two forms to which we have attached special importance, gave much less definite results. Some of the animals have not yet, however, been examined microscopically. Control animals fed with other organisms gave quite negative results. These experiments have at least shown that diphtheroid bacilli isolated from cases of general paralysis may occasionally have sufficient virulence to determine in rats, by infection through the alimentary tract, a disease in which the chief symptoms are those affecting the nervous system, and in which the tissue changes have a certain resemblance to those found in general paralysis.