698 



SCIENCE 



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



convulsive seizures which come on sud- 

 denly. A given virus has up to the present 

 been sent through a series of six rabbits, 

 after which it has failed to be further 

 propagated. From the sixth series it has 

 been reimplanted on the monkey, in which 

 animal typical paralysis has been pro- 

 duced. It remains to add that the rabbits 

 which succumb to the inoculation do not 

 show any characteristic alterations of the 

 central nervous system or other organs, as 

 far as has been determined. The monkey, 

 on the other hand, invariably shows the 

 typical lesion of the central nervous system. 

 Long before epidemic poliomyelitis had 

 the wide distribution or claimed the atten- 

 tion now accorded it, instances of infantile 

 paralysis were known to every one. Almost 

 every community could point to one or 

 more examples of the condition and no one 

 entertained the suspicion that the cause of 

 the paralysis was an infectious or even con- 

 tagious disease. Are these isolated cases 

 of paralysis occurring among infants of 

 the same nature as the epidemic paralysis, 

 or has there merely been a confusion of 

 names? We possess means that permit an 

 answer to this important question. Recov- 

 ery, as you recall, is associated with en- 

 during immunity and the person or animal 

 immune to poliomyelitis carries in his blood 

 principles that neutralize the virus causing 

 the disease. The blood of normal persons 

 or animals lacks this property in any real 

 degree. The test is, therefore, easily made : 

 a mixture of the serum of the blood and 

 virus are prepared, and after being in con- 

 tact for a time is injected into a monkey. 

 Thus it has been determined that the two 

 diseases are caused by the same parasite, 

 and it has been found that the neutralizing 

 principles are still present as long as 

 twenty-five years after the attack of paral- 

 ysis and doubtless persist through life. 



This test has been employed likewise to 

 identify abortive eases of poliomyelitis in 

 which paralysis has not appeared a^ all. 



There is nothing unique in this appar- 

 ently paradoxical situation. Most, if not 

 all, epidemic diseases prevail at some time 

 as sporadic affections; that is, as dis- 

 eases of occasional occurrence. This is 

 true of influenza, plague and particularly 

 of meningitis, with which poliomyelitis dis- 

 plays so many affinities. Knowledge is 

 still very imperfect as to just what hap- 

 pens when an epidemic spread of a spo- 

 radic disease takes place. Sometimes con- 

 ditions arise that favor rapid transference 

 of the infecting microbe from individual 

 to individual through which a rise in viru- 

 lence is accomplished very much as is done 

 every day in the laboratory to enhance the 

 potency of cultures. In respect to polio- 

 myelitis, as seems also to be the case with 

 meningitis, a fresh importation of an al- 

 ready enhanced virus probably occurs and 

 is the immediate cause of the epidemic. 

 The introduction may be at one point or at 

 several points simultaneously, according to 

 where the epidemic arises, and spreads 

 from a single center or from many foci. 

 Finally, sports, or abnormally virulent 

 parasites, appear, prevail actively for a 

 period and then become reduced to an 

 average degree of intensity perhaps never 

 to rise again. Some of the exceptionally 

 severe epidemics of which history tells us 

 may be thus accounted for. Such sports 

 have been encountered in laboratories in 

 regard to both pathogenic bacteria and 

 protozoa. 



Are biologically different strains of a 

 poliomyelitic virus known? The evidence 

 at hand is to the effect that different 

 strains or races certainly exist if virulence 

 be taken as the measure. German, Aus- 

 trian and French pathologists found that 



