These failures led many to the belief that poliomyelitis is a toxaemia. Experimental investigation has now proved the incorrectness of this belief. The virus occurs in the spinal cord. By injecting virulent material into the brain the spinal cord is made virulent and we can then reproduce the disease in monkeys by intracerebral inoculation with this virulent spinal cord tissue. The virus has thus been propagated through many generations of monkeys.
The virus shows a special affinity for the spinal cord. Wherever it be injected it will be found mainly localized in that organ. But it has not been demonstrated in the blood, spleen or any other organ of the monkey. Yet it seems to be eliminated by several channels, for after intracerebral injection it has been found in the salivary and mesenteric glands and in the nasal mucous membrane. In the spinal cord its potency is preserved for some time but soon diminishes and finally disappears; at least Levaditi and Landsteiner observed that the spinal cord about six weeks after infection was no longer virulent.
The interesting fact has, moreover, been established that the virus of acute poliomyelitis cannot be classed among the common bacteria, for it passes through bacterial filters such as the Berkfeld. When fluid containing ordinary bacteria is so filtered, the filtrate is sterile: in poliomyelitis the filtrate is infective; hence the virus belongs to that class which we usually designate filtrable. It closely resembles, in many of its characters, the virus of rabies. One property which both enjoy is resistance to the action of glycerin. This resistance distinguishes them from all ordinary bacteria. Römer and Joseph found the virus after almost five months in undiluted glycerin potently infective; but other observers have recorded an attenuation of the virulence under similar conditions.
The poliomyelitis virus is also markedly resistant to other agents. Flexner and Lewis, for example, found the infectivity still preserved after exposure for forty days to a temperature of from -2° to -4° Celsius; and, after fifty days, at -4° C. During the exposure autolysis appeared in the preserved pieces of the cord which were covered with mould, and yet the virus remained unimpaired. Even to drying, the virus is most resistant. The experiments of Leiner and von Wiesner show, however, that
