EPIDEMIC POLIOMYELITIS 683 



along the vessels which may become thrombosed and may also 

 rupture. The nutrition of the grey matter is thus interfered 

 with, the nerve cells may die and become the prey of neurono- 

 phages, and secondary local and systemic degenerations may 

 follow. Such a pathological picture, however, is not confined to 

 the grey matter nor indeed to the cord, as similar changes have 

 been observed in the brain. The recognition of this has 

 widened the whole conception of the disease, and various 

 clinical types besides the classic anterior poliomyelitis are now 

 recognised to exist. These depend partly on variations in the 

 severity of the condition, partly on the fact of the disease being 

 concentrated in a particular part of the nervous system. These 

 less common types probably include the acute ascending 

 paralysis of Landry, acute bulbar paralysis, cases characterised 

 by acute meningitis or encephalitis, cases of rapidly developing 

 ataxia, and even cases simulating neuritis. 



The infectivity of the disease was established by the work of 

 Landsteiner and Popper, who in 1909 in Vienna succeeded in 

 producing the disease in a monkey by the intraperitoneal 

 injection of an emulsion of the spinal cord of a child who had 

 succumbed on the fourth day of illness. Similar observations 

 were made in the same year by Flexner in New York, who 

 found that if for intraperitoneal injection intracerebral inocula- 

 tion was substituted, disease results were more uniformly pro- 

 duced, and the brain and cord of the infected animals were 

 infective for other monkeys, the incubation period being from 

 4 to 33 days. It is on the work of Landsteiner, Levaditi, and 

 especially of Flexner that our present knowledge is chiefly based. 

 Hitherto the monkey is the only animal to which the disease has 

 been communicated, both the anthropoid apes and the lower 

 monkeys are susceptible, and the conditions resulting from inocu- 

 lation are clinically and pathologically identical with those 

 observed in man. All attempts to isolate a definite causal 

 agent have been unsuccessful, and as emulsions of infective 

 organs filtered through a Berkefeld filter retain their infectivity, 

 it has been established that in poliomyelitis we have another 

 example of an ultra-microscopic virus. 



In infecting monkeys from a human case it is advisable to 

 commence with the use of an emulsion of the central nervous 

 system, for filtered emulsions possess less virulence ; but after a 

 few passages through monkeys it is found that filtration has 

 little effect in diminishing the number of successful inoculations, 

 the virus being now so potent that from O'OOl to O'Ol of 1 c.c. of 

 an emulsion of the spinal cord in distilled water will originate 



