Immunization of Monkeys against Poliomyelitis. 99 



suspension from monkey poliomyelitis is subjected to 55 0 C. for 

 one half hour and injected subcutaneously into monkeys on ten 

 successive days. This represents the use of killed virus. In the 

 other method the 10 per cent, emulsion is subjected to graded 

 attenuation as follows: heated to 55 0 C. for one half hour on first 

 two days; to 45 0 C. on third day; to 37 0 C. on fourth day and on 

 the fifth day the material is injected unheated. 



On the 20th day after the series of subcutaneous injections 

 are completed, the treated animals are bled from the heart in order 

 to test for the presence of neutralizing substances in the blood. 

 On the following day the treated animals were tested by subjecting 

 them to three to five intracerebral lethal doses of highly potent 

 monkey virus. The sera of the treated animals were placed in 

 contact with equal part of 5 per cent, emulsion of monkey virus 

 at 37 0 C. for two hours and then in ice box over night. On the 

 day of intracerebral test for treated animals, the serum virus 

 mixtures were inoculated intracerebrally into normal monkeys. 

 The same virus emulsion was used in the test inoculations and 

 serum virus mixtures. 



The results with killed virus injection method were not so 

 good as with that of graded attenuation. In the former method 

 only 3 animals were used. Of these two succumbed to test 

 inoculations with the usual incubation and the third presented a 

 delayed incubation of 12 days, but recovered with residual 

 paralyses of both arms and legs. The serum of one of these com- 

 pletely neutralized virus; in another the incubation was prolonged 

 to 18 days but animal recovered and now presents residual 

 paralysis of legs; in the third the incubation was prolonged to 10 

 days and animal died. The incubation periods of two normal 

 controls were 5 and 6 days respectively. 



Of eleven animals subjected to injections by the graded 

 attenuation method, none showed any ill effects from the treat- 

 ment itself. Five out of eight subjected to the intracerebral test 

 injection of from 3 to 6 lethal doses resisted successfully. Sera of 

 all the animals tested demonstrated the presence of neutralizing 

 substances. Three completely neutralized 5 per cent, emulsion 

 of highly potent virus in proportion of 1 : 1. Four others delayed 

 the four- and five-day incubation periods of normal controls to 



