244 Chapter VIII 



of fresh unvaccinated rabbits. When, however, he injected cultures 

 grown in the serum of immunised animals into rabbits, these rabbits 

 did not die and presented only transient and insignificant lesions. 

 From this fact Roger concluded that there must be an attenuation 

 of the streptococcus by the immune serum, a view which was shared 

 by several other observers. In formulating this view, however, he 

 had not taken into account the possibility that this serum acted not 

 upon the coccus that had developed in it but upon the organism 

 of the animal into which it was injected. Bordet 1 , indeed, was able 

 to show that the streptococcus which grows in the serum of im- 

 munised animals is in no way weakened in virulence. When he 

 took a race very virulent for the rabbit (Marmorek's streptococcus) 

 and injected a minimal dose of a culture grown in the serum of 

 immunised animals, the rabbits died just as did the control animals, 

 because the amount of serum introduced was too small to exert 

 any influence. So also, when he filtered this culture and got rid 

 of the serum bathing the streptococci, it was found to be just as 

 [257] virulent as that grown in the serum of susceptible unvaccinated 

 animals. 



In confirmation of the discovery made by Roger with the serum 

 of vaccinated rabbits, Bordet showed that the blood serum of horses 

 highly immunised against the streptococcus did not exhibit any 

 bactericidal action. Moreover, he found that this serum caused the 

 development of somewhat agglutinated streptococci and that it was 

 capable of throwing streptococci grown on the ordinary media into 

 clumps. Summing up his researches on the properties of this serum 

 Bordet concludes that it " causes no profound change in the strepto- 

 coccus. The vegetative character of the coccus is not appreciably 

 diminished, and its morphology remains the same save for certain 

 variations in the length of the chains. Even the agglutinative 

 power, recognised in numerous serums by recent researches, is, in 

 the antistreptococcic serum, developed but slightly" (p. 196). 



More recently von Lingelsheim 2 has studied the properties of 

 the serum of animals which he had thoroughly vaccinated against 

 the streptococcus. He observed a certain slowing of the development 

 of the coccus in this serum as compared with the growth in cultures 

 made in the serum of normal, susceptible animals. But this re- 



1 Ann. de VInst. Pasteur, Paris, 1897, t. xi, p. 194. 



3 Arch, internal, de Pharmacodyn., Gaud et Paris, 1899, Vol. vi, p. 73 ; Behring's 

 Beitr. z. experim. Therapie," 1899, Bd. t 



