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4 others, we must conclude that the cause of acute poliomyelitis does not belong to the class of the common bacteria, but is a filterable virus, and is present in the spinal cord.

Epidemic and Sporadic Acute Poliomyelitis.—It may not be inappropriate to refer here to the relation between epidemic and acute poliomyelitis. Some assert that both conditions are not identical. The following are the principal reasons for this assertion: (a) the clinical picture of Heine-Medin's disease is much more variable than that of the classical infantile paralysis; (b) in a number of cases of the former disease the cranial nerves are specially involved, whereas cranial nerve lesions usually do not occur in infantile paralysis; (c) adults are more liable to be attacked in epidemic poliomyelitis; (d) sporadic poliomyelitis seldom runs a lethal course, whereas the epidemic variety has a considerable mortality; (e) and, finally, the epidemic occurrence itself is a characteristic distinction.

The difference in symptomatology is more apparent than real. Obviously very different opportunities for clinical observation exist when hundreds of cases can be examined together than when only isolated cases are available from year to year. In epidemics, connections can be clearly traced between symptom complexes, which in isolated cases may appear unrelated, and the fact must be emphasized that the spinal type (the classical infantile paralysis) forms the nucleus of Heine-Medin's disease. From the most recent observations as to the localization of the paralysis, it is evident that the extremities—especially the legs—are oftenest affected. No doubt of the complete correspondence of the disease with the ancient infantile paralysis can endure. The changes in the acute and chronic stages have been shown to be absolutely identical in both. Netter and Levaditi have procured further and remarkably interesting evidence. They were able to prove in a case of sporadic acute poliomyelitis in which the acute stage had occurred three years previously, that the serum "in vitro" destroyed the virus of the epidemic poliomyelitis.

I wish, nevertheless, to refer here to certain peculiarities of Heine-Medin's disease, and to some circumstances which may explain why the epidemic and the sporadic forms have been regarded as distinct.

Heine-Medin's disease shows a striking variability which is