694 



SCIENCE 



[N. S. Vol. XXXVI. No. 934 



hence in order that it shall be capable of 

 propagating poliomyelitis, it must secure a 

 means of escape from the infected animal. 

 The escape is now known to occur along 

 with the secretions of the nose and throat, 

 and the discharges from the intestine. We 

 are obliged, therefore, to ask ourselves what 

 the means are by which the virus confined 

 within the interior reaches these external 

 surfaces of the body. 



Let us begin by disregarding for the 

 moment the essential point of the way in 

 which the virus probably enters the body 

 in infected human beings, and give our 

 attention to the way in which it escapes in 

 the infected monkey into the nose, throat 

 and intestines. We may first consider the 

 instance in which the virus is deposited in 

 the brain, in which it becomes sealed, as it 

 were, and cut off apparently from the ex- 

 terior of the body. Having been injected 

 into the brain, the infectious microorgan- 

 ism constituting the virus multiplies both 

 within and about the brain tissue at the 

 site of inoculation. As multiplication 

 progresses, the virus leaves the original 

 site of injection and wanders through ad- 

 jacent and distant parts of the central ner- 

 vous tissues, becoming implanted in the 

 medulla, the spinal cord and the inter- 

 vertebral ganglia, as well as reaching the 

 pia-arachnoidal membranes, or meninges, 

 in which it also spreads. Ultimately, when 

 the virus becomes sufficient in amount, it 

 brings about anatomical changes in the 

 nervous system, one of the results of which 

 is paralysis. The period intervening be- 

 tween the inoculation and the appearance 

 of paralytic symptoms may be as brief as 

 two or three days, or as long as three, four 

 or five weeks. The great disparity in this 

 period depends upon the amount and qual- 

 ity of the virus, as well as the degree of 

 resistance of the inoculated monkey. 



The virus, which has found its way to 

 the meninges, does not long remain in the 

 cerebrospinal fiuid, with which it escapes 

 in part into the blood, where it does not 

 appear to undergo any further increase in 

 amount, and indeed seems even incapable 

 of surviving for long. A part also of 

 the virus contained within the cerebral 

 fluid escapes regularly by way of the 

 lymphatic channels surrounding the short 

 nerves of smell that pass from the olfac- 

 tory lobes of the brain to the mucous mem- 

 brane of the nose. It has long been known 

 that there is an intimate connection be- 

 tween the lymphatic vessels of the nasal 

 mucous membrane and the lymphatic 

 spaces of the pia-arachnoidal membrane. 

 The virus once having gained the mucous 

 membrane of the nose may even escape 

 into the mucus secretion, with which it is 

 carried into the mouth, and in part swal- 

 lowed, or it may become established in the 

 substance of the nasal membrane, where it 

 undergoes subsequent multiplication and 

 increase. As a matter of fact both these 

 things occur. The virus escapes with the 

 secretions partly externally to the infected 

 body, and a part of it is swallowed with 

 the secretions themselves, while a persistent 

 infection of the secretions is maintained 

 by means of the increase that takes place 

 in the membrane itself. In this way is 

 assured the escape of the virus directly 

 into external nature, as well as the con- 

 tamination of the gastro-intestinal cavity, 

 with the discharges of which it becomes 

 commingled. Once implanted upon the in- 

 testine multiplication not improbably con- 

 tinues for a time, and another source of 

 invasion of the body is thus afforded the 

 parasite. From the intestine it reaches in 

 some amount the mesenteric lymph nodes, 

 and thus enables us to account for the 

 occurrence of the virus in those lymphatic 



