THE PROBLEM OF VIRULENCE 19 



and more apparent whereas the diminution of virulence which 

 takes place on artificial media is accompanied by a gradual loss -of 

 capsule formation. Organisms like the Friedlander bacillus which 

 retain their ability to form capsules almost indefinitely in artificial 

 culture moreover do not lose their virulence to any great extent as 

 long as this property is preserved. It is also well known that cap- 

 sulated bacteria are peculiarly insusceptible to the ordinary aggluti- 

 nating powers of specific immune sera. This has been noticed, not 

 only in the case of heavily capsulated bacteria like those of the Fried- 

 lander group or the streptococcus mucosus, but, in the case of plague 

 bacilli where capsulation is usually present only in cultures taken 

 directly from the animal body and cultivated at 37 C., Shiba- 

 yama 27 has found a direct relation between non-agglutinability and 

 a slimy condition of the cultures. Cultures kept at 5 to 8 C. in 

 the ice-chest were easily aggiutinable and lacked the slimy property. 

 Cultures kept at 37.5 C. were slimy and thready in consistency and 

 were not as easily agglutinated by the same immune serum. 

 Forges 28 later showed that inagglutinable, capsulated bacteria can 

 be made amenable to the agglutinating action of the serum which 

 we may assume to indicate vulnerability by the serum if the capsule 

 is previously destroyed by heating at 80 C. for about 15 minutes in 

 !/4 normal acid. 



Against the cellular defences, the leukocytes, capsulated bacteria 

 seem also to be more resistant than are the non-capsulated. This 

 has been especially studied by Gruber and Futaki, 29 who find that a 

 capsulated bacillus is rarely taken up by a phagocyte even when 

 these cells are apparently normal and able to take up the uncap- 

 sulated organisms. They go so far as to claim that, in the case of 

 anthrax in rabbits, the development or absence of a capsule deter- 

 mines whether or not infection can take place. The same conclusion 

 is reached in similar studies by Preisz, 30 who does not believe that 

 anthrax bacilli can ever cause infection unless they possess the 

 power of forming capsules. All this experimental evidence points 

 strongly toward a probable direct relationship between capsule for- 

 mation and virulence, in the sense that a thickening of the ectoplasm 

 may in some way protect the bacteria from the destructive forces 

 aimed at them by the cells and fluids of the invaded body. 



As a matter of fact, even when no distinct capsule is visible, it 

 is nevertheless possible that ectoplasmic changes may take place. 

 This phase of the subject has been thoroughly discussed by a number 

 of writers, more especially by Eisenberg. 31 It appears that many 



27 Shibayama. Centralbl. f. Bact., Orig. Vols. 38, 1905, and 42, 1906. 



28 Forge's. Wien. klin. Woch., p. 691, 1905. 



29 Gruber and Futaki. Munch, med. Woch., 6, 1906. 



30 Preisz. Centralbl f. Bakt., Vol. 49, 1909. 



81 Eisenberg. Centralbl. f. Bakt., I, 45, 1908, p. 638. 



