NATURE OF VIRUS 685 



lymphatics, the existence of which is reflected in the appearance 

 of such cells in moderate numbers in the cerebrospinal fluid. In 

 the cord the inflammatory condition is usually marked in the 

 arterioles of the anterior commissure, especially in the cervical 

 and lumbar regions, and thence passes into the anterior cornua 

 along the vessels, which show intense hyperaemia with peri- 

 vascular cell proliferation and which may become thrombosed 

 or 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, arid 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 many cases described as 

 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 

 certainly been communicated, — both the anthropoid apes and 

 the lower monkeys are susceptible, and the conditions resulting 

 from inoculation are clinically and patholbgically identical with 

 those observed in man. 



With regard to the nature of the virus the discovery was made 

 independently by Flexner and Lewis, and by Landsteiner and 

 Levaditi, that it could pass through an earthenware filter 

 {e.g., Berkefeld N or V). The deduction from this observation 

 was that the causal organism must be very small, and Flexner 



