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PATHOLOGY: S. FLEXNER 
MECHANISMS THAT DEFEND THE BODY FROM POLIOMYELITIC 
INFECTION, (a) EXTERNAL OR EXTRA-NERVOUS. 
(b) INTERNAL OR NERVOUS 
By Simon Flexner 
ROCKEFELLER INSTITUTE FOR MEDICAL RESEARCH 
Read before the Academy April 17. 1917 
I am led to report the results of recent experiments looking toward 
the solution of the problem of susceptibility in epidemic poliomyelitis, 
by reason of the intriasic interest of the subject and because of certain 
advances in knowledge which have been made recently. 
The mass of the population appears insusceptible to the disease. That 
is to say even under conditions in which poliomyelitis is severely epi- 
demic the real incidence is low. Thus the incidence during the past 
summer and autumn in Greater New York City, in which more 
than 9000 cases of the disease were recognized, was L59 per 1000 of the 
population. 
Our present knowledge indicates that during epidemics, the microbic 
cause or virus of the disease is very widespread. This virus leaves and 
enters the body by way of the nasal and buccal mucous membranes. It 
is present not only in paralyzed persons but equally in the greater num- 
ber of the affected who are often only sHghtly ill and do not develop any 
paralysis whatever, and in an undetermined number of healthy persons 
who have been in intimate contact with both classes of patients 
mentioned. 
In view of the wide distribution of the virus and the relatively low case 
incidence, we must suppose that many more persons are exposed to 
than acquire the infection. Hence the body must possess defensive 
mechanisms usually sufficing to protect it from invasion. 
Two sets of defences have been detected. The first or external con- 
sists of the secretions of the nasal and probably pharyngeal mucous 
membranes. Their action has been especially studied by Amoss and 
Taylor.^ The secretions in many if not in most persons when left in con- 
tact for a relatively short time with the virus of poliomyelitis, inactivate 
or neutralize it. This test is readily made because monkeys are highly 
susceptible to inoculation with the virus. When an active virus has 
been mixed with the bacteria-free nasal secretions obtained by filtration 
through porcelain, it is no longer active for monkeys. 
Some persons fail to yield this neutralizing nasal secretion; in others, 
a temporary, pathological state of the mucous membranes removes the 
inactivating property previously present. The number of tests is still 
