XX] CAUSAL AGENT 367 



observations on the development of the virus within the body 

 of an infected subject. 



The disease is essentially one of the central nervous system 

 as evidenced by both the clinical and pathological features of 

 the infection. If the virus is injected into the sciatic nerve of 

 a monkey, it has been shewn that it multiplies in the nerve, 

 first at the site of the injection and then progresses along the 

 nerve until it reaches the spinal cord, when it causes paralysis 

 of the hind-quarters. When the virus is placed on the unin- 

 jured nasal mucous membrane, the infective agent travels up 

 the olfactory nerves and subsequently causes general paralysis. 

 It is evident, therefore, that nervous tissue is the one in which 

 the organism chiefly multiplies. From the brain and spinal 

 cord it passes into the cerebro-spinal fluid and thence into the 

 blood circulation and lymphatic system, but in these positions 

 it does not seem to persist for any length of time, except in the 

 lymphatic nodes. The presence of the virus in the lymphatics 

 explains why the nasal secretion becomes infected, for it has 

 been shewn that poliomyelitis escapes with the secretions of the 

 nose and throat and the discharges from the intestine of an 

 infected person. 



Method of infection. Considering the infectivity of the 

 various secretions of a patient suffering from poliomyelitis, it 

 is only reasonable to suppose that the disease may be directly 

 transmitted from one person to another without the aid of 

 any intermediate host. Flexner supports the view that the 

 nasal mucous membrane is the chief site of infection, for the 

 virus is able to survive in the form of dust and thus might be 

 inhaled, and, in fact, the sweepings of a room occupied by a 

 poliomyelitis patient have been shewn to be infected. 



On the other hand, as a result of very thorough epidemio- 

 logical studies conducted by the Massachusetts State Board 

 of Health, evidence has been collected which supports the 

 theory that the disease is spread by insects. Rosenau has 

 recently (1912) been able to transmit poliomyelitis from infected 

 to healthy monkeys by the bites of Stomoxys calcitrans. Several 

 monkeys infected with the disease by intracerebral inoculation 

 were daily exposed to the bites of several hundred Stomoxys, 



