IOO 



Scientific Proceedings (91). 



from 10 to 25 days. To indicate potency of test virus two animals 

 that had recovered from previous experimental infection and which 

 presented residual paralyses succumbed as readily as the normal 

 controls to the intracerebral injection of only three times the dose 

 used to test the treated animals. Animals that have recovered 

 from experimental infections have been found to be highly re- 

 sistant to reinfection. 



The latter method requires only a short time; the material 

 is easily produced and gives a considerable degree of immunity. 

 The test method is far more severe than that to which persons 

 are subjected in the natural infection inasmuch as in this artificial 

 test the defensive forces in the blood stream are circumvented, 

 whereas in the natural infection the infective material would first 

 come in contact with the neutralizing substances present in the 

 blood stream before it could gain entrance to the central nervous 

 system. The natural infection is far less severe than the experi- 

 mental disease in which we may have a mortality of about 99 

 per cent. 



168 (1346) 



Persistence of immunity following toxin-antitoxin injections. 

 By William H. Park. 



[From the Bureau of Laboratories Dept. of Health, N. Y. C] 



During the past years, we have immunized a series of guinea 

 pigs and a series of horses and a series of children with diphtheria 

 toxin-antitoxin mixtures. The duration of the immunity presents 

 certain points of great interest. So far as our observation goes, 

 guinea pigs are never naturally immune; horses in the very great 

 majority of cases are immune; adults and infants under 6 months 

 are immune to 80 per cent., while very young children are non- 

 immune to about 60 per cent. We find, in the guinea pig, that 

 active immunity lasts for about nine months. In horses, we find 

 the increased immunity, due to the injections, lasts from nine 

 months to twelve months, at which time the horses return to their 

 original amounts of natural antitoxic immunity. 



In testing human beings from month to month, it was a matter 

 of great interest to find whether the infants and children who be- 



