684 EPIDEMIC POLIOMYELITIS 



the disease when injected into the brain. Such a virus with- 

 stands glycerination for weeks and can be kept frozen at - 2 to 

 - 4 C. without being affected. It also withstands from 1 to 

 1J per cent, phenol for at least five days; it is, however, killed 

 by an exposure at 45 to 50 C. for half an hour. The disease 

 can be originated by subdural and intracerebral injection, and 

 also by introduction into the sheath of such a nerve as the 

 sciatic, and the intraperitoneal and subcutaneous methods can 

 also be employed ; the best results are obtained by combining 

 intracerebral and intraperitoneal injection. When the sheath of 

 a nerve is infected, the paralytic symptoms first appear in relation 

 to that part of the cord from which the nerve emerges. Infec- 

 tion can also readily be produced by scarifying the mucous 

 membrane of the nose and rubbing the virus into it. Whatever 

 the path of infection, the chief concentration of the virus is in 

 the central nervous system of the animal. It also occurs in the 

 lymphatic glands, and especially in the tonsils. It is absent 

 from the solid organs, the blood, and the cerebro -spinal fluid. 

 It is important to note that after intracerebral infection the 

 nasal mucosa is found to be very infective, the virus being thus 

 eliminated into the naso-pharnyx. In human cases the virus is 

 again chiefly concentrated in the central nervous system, but it 

 has been found in the tonsils, the mesenteric glands, the pharyn- 

 geal mucosa, the nasal mucous secretions, and in the intestinal 

 contents. In experiments with emulsions of exposed surfaces 

 and with secretions, the filterability of the virus and its resist- 

 ance to phenol are important, as means are thus at hand for 

 eliminating the action of adventitious bacteria. 



Though no cases are recorded of a second attack of poliomyel- 

 itis in man, our knowledge regarding immunity is mainly derived 

 from animal experimentation. Monkeys which have passed 

 through an attack of the disease are insusceptible to fresh 

 inoculation, but previous disease manifestations are apparently 

 essential to the establishment of immunity, as animals which 

 have at first yielded negative results are usually susceptible to 

 a second inoculation. Both in man and in the monkey the 

 serum of a recovered case contains substances capable of neutral- 

 ising the virus, for if such serum be mixed with virus and 

 incubated for a time at 37 C. the mixture becomes inopera- 

 tive on intracerebral injection into monkeys. The antibodies 

 persist in the serum in man for many years after an acute 

 attack, and they possess this further significance, that they may 

 be found in the so-called abortive cases where a transient illness 

 with little or no involvement of the nervous system occurs. The 



