584 EXPEKIMENT STATION EECOBD. 



(Rhode Island Sta. Bxil. 150, pp. Sl-161). — This continues work previously noted 

 (E. S. K., 26, p. 185). 



"Among 10 different strains of the fowl cholera bacterium investigated for 

 their resistance-producing power, one (culture 52) was discovered which was 

 capable of producing perfect immunity in rabbits to highly virulent cultures; 

 this immunity was secured by means of subcutaneous, intravenous, and also 

 intraperitoneal inoculations. That the resistance in question was not a local, 

 or ' zonal,' Immunity, was shown by inoculating previously protected rabbits 

 in the ear, flank, or back, also by intravenous and intraperitoneal inoculations, 

 none of which were fatal. The smallest amount of culture 52 yet used to 

 produce immunity in rabbits is 0.000,000,01 cc. ; but amounts as large as 3 cc. 

 were tolerated, and gave similar results. Smaller amounts would, in all prob- 

 ability, also afford resistance. The resistance produced by inoculation with 

 culture 52 was sufficiently strong to protect against at least 2 cc. of virulent 

 culture when the M. L. D. [minimum lethal dose] of the latter was 

 0.000.000,000,000,000,000,01 (one-hundredquintilliouth) cc. 



"In protectively inoculated rabbits a slight resistance was manifested within 

 2 to 4 days, but complete immunity did not appear until the seventh day after 

 the inoculation with culture 52. Complete immunity to the virulent culture 

 (48) has been found to endure in protected rabbits for at least 10 months; it 

 is, in all probability, permanently acquired. The simultaneous inoculation of 

 culture 52 (amounts from 0.001 cc. to 1 cc.) and culture 48 (0.001) proved 

 fatal in all cases; but the inoculation of 0.5 cc. of culture 52 prevented a fatal 

 termination when inoculated simultaneously with 0.000.000,001 cc. of culture 

 48. Attempts to produce resistance in rabbits by the inoculation of dead or 

 attenuated (by heating) cultures of strains 52 and 48 have thus far failed, 

 except with repeated inoculation of 52. Immunity to culture 48 is inherited: 

 Does, G to 7 months after their protective inoculation, have given birth to young 

 possessing, at the age of 30 days, complete resistance to 0.01 cc. of the virulent 

 culture; but no cases have been met with in which the young, at the age of 

 60 days, were still immune. 



" The natural resistance possessed by guinea pigs to the fowl cholera organism 

 can be so raised by subcutaneous inoculation with culture 52, that both subcu- 

 taneous and intraperitoneal inoculations with the virulent culture (48) are 

 easily tolerated. Although gray rats ai'e susceptible to fowl cholera, the strain 

 of white rats used in this investigation possessed a high degree of natural im- 

 munity. In a few preliminary tests a moderate degree of resistance in pigeons 

 and fowls to a virulent culture of the fowl cholera bacterium has been produced 

 by intramuscular, and (more successfully) by subcutaneous, inoculations with 

 cultui-e 52 ; but this method, for birds, is as yet somewhat less reliable than 

 for rabbits. Inoculation with culture 52 has been found to protect rabbits, not 

 against virulent culture 48 alone, but also against the only other (three) highly 

 virulent cultures obtainable at the present time. In two cases, as the result 

 of a single subcutaneous inoculation with 0.5 cc. and 1 cc, respectively, of 

 serum, derived from an actively inmiunized rabbit, 9 months after immuniza- 

 tion, the fatal issue in the infected rabbits was delayed from 14 hours (control) 

 to 4 and 5 days, respectively. Many of the phenomena observed in this study 

 make it appear that the immunity being considered is an aggi-essin immunity 

 in the sense in which this term is employed by Bail, Weil, and others. But 

 the observation that various attenuated cultures, all of which possess about the 

 same ability to grow at the point of inoculation (implying, according to this 

 theory, approximately equal 'aggressiveness') demonstrate by no means equal 

 resistance-producing powers, suggests that the aggressins and ' anti-aggressins ' 

 do not wholly explain the production of immunity in these cases. These inves- 



