The experimental data collected during this study of a transmissible type of paralysis developing in tuberculous guinea pigs indicate the condition to be a true tuberculous meningitis. We have been able to rule out the possibility that it is due to a non-tuberculous infection of the central nervous system caused by Roemer's virus, or by an atypical herpes virus, or by some bacterium other than the tubercle bacillus. Roemer's virus and herpes could be eliminated from consideration when Berkefeld N filtrates of infectious brain emulsions proved incapable of reproducing the disease. Furthermore, rabbits could be infected as they cannot with Roemer's virus, and the disease elicited in rabbits bears no semblance to herpes encephalitis. No organism other than the tubercle bacillus could be obtained on culturing brain or brain emulsions from experimental cases, and no others were seen in examining fresh smear preparations from the central nervous system. In a modified Noguchi medium a tubercle bacillus possessing atypical staining properties was obtained. This organism was capable of producing the typical paralytic disease when injected intracerebrally into guinea pigs, and also generalized tuberculosis in animals inoculated subcutaneously with it.
Typical tuberde bacilli were readily demonstrable in sections of the meninges from animals with the disease, and culture of pieces of brain on Dorset's egg medium usually yielded a growth of tubercle bacilli. Only in the first of the experimental passages, on the other hand, was it possible to demonstrate acid-fast organisms in fresh smear preparations from the central nervous system. This fact and the attributes of the atypically staining organisms encountered in the cultures in Noguchi media will be considered more fully in a subsequent publication.
In view of the much discussed question of the filtrability of the tubercle bacillus our observations concerning the failure of this organism to pass a Berkefeld N filter are of interest. No animal in our series inoculated intracerebrally with brain emulsion from either a "spontaneous" or experimental case of tuberculous meningitis failed to develop meningitis, and that rather acutely, while no animal in our series injected with a Berkefeld filtrate of brain emulsion has developed tuberculous meningitis or any other form of tuberculosis. In connection with this observation it must be recalled that the organism was atypical in respect to its staining qualities at least.