ACUTE POLIOMYELITIS. 303 



showed that Pohomyelitis is not as we were heretofore lead to believe caused 

 by different kinds of micro-organisms, but by a specific virus which can. not 

 be demonstrated by the ordinary bacteriological methods. This work 

 gave impetus to a host of experiments upon monkeys and made it possible 

 for the previously mentioned authors and Flexner, and Lewis, and Levaditi 

 to carry out successive animal passages. These experiments also demon- 

 strated that the virus was filterable and resistent toward glycerin and in 

 these respects resembled the virus of Rabies. 



Uniformly negative results are obtained when mice, rats, guinea-pigs, 

 cats, dogs, sheep, goats, pigs, horses, calves, chickens, and doves are injected. 

 Of the different species of monkeys used for this work the macac cynomol- 

 gus seems to be the most susceptible. This is especially true of young, half- 

 grown animals. The symjitoms of infected monkeys are essentially the same 

 as those of the human type of the disease. According to the experiments 

 conducted by Flexner and Lewis the inoculf>tion is followed by a symptomless 

 incubation period which may be from two to forty-six days, usually one or 

 two weeks in duration. This latter is largely dependent upon the size and 

 virulence of the test dose. The incubation period is followed by premoni- 

 tory symptoms which consist of nervousness, shaking of the head and of 

 the extremities, general weakness, spasmodic condition, and possibly uncon- 

 sciousness, followed in a comparatively short time, from a few hours to one 

 or two days, by the characteristic paresis and crippling. Paralysis of the 

 hind quarters, seldom front, follows and in sever cases the muscles of the 

 trunk, neck, and back are affected and the animals die with disturbed breath- 

 ing. The disease is much more fatal for monkeys, seventy-six per cent, than 

 for humans, five to twenty per cent. Flexnor and liewis noticed that some 

 of the monkeys after intraperitoneal or subcutaneous injection of the sus- 

 pected material developed no paralysis but showed marked signs of drowsi- 

 ness, weakening, and diarrhea. However, if fresh clean monkeys were in- 

 jected with spinal cord suspensions which were obtained from these latter 

 eases, they would become infected with the typical type of the disease. 

 From analogy, in all probability we have the same occurring in humans; also 

 it is quite probable that monkeys may suffer from the abortive type as man 

 does. 



By injecting j'ouny rabbits of a certain species with enormous doses Marks 

 was able to infect and to pass the virus successfully from rabbit to rabbit. 

 Marks also produced typical infection in monkeys by injecting the latter 

 with the virus which had undergone successive rabbit passage. 



The infected rabbits died between the eighth and tenth days and just 

 before death showed symptoms of weakness and cramps. However, char- 

 acteristic pathological changes were not found on post-mortem. Therefore, 

 that rabbits are susceptible to the virus, although not developing the charac- 

 teristic symptoms, can be demonstrated by injecting the rabl)it strain into 

 monkeys, the latter develop the characterislics of the disease. 



