168 Chapter VI 



be regarded as absolutely demonstrative. Thus, Marchand observed 

 [178] that the attenuated streptococci, when conveyed in the culture- 

 fluid of the virulent variety, are as readily devoured by the phago- 

 cytes as when they were injected alone. According to him, there- 

 fore, there was in the culture-fluid of the virulent streptococcus 

 no soluble substance capable of exciting the negative chemiotaxis 

 of the leucocytes. But is it quite proved that this substance must 

 necessarily pass into the filtrate of a virulent culture ? If it adheres 

 closely to the glairy aureola, as we have suggested, may it not remain 

 behind with the bodies of the streptococci, without passing through 

 the filter in any appreciable amount? The question cannot be re- 

 garded as definitely settled, but probability appears to be on the side 

 of the theory of chemiotaxis. 



Marchand also investigated whether the immunity against the 

 attenuated streptococcus might not be explained by the bactericidal 

 activity of the fluids of refractory animals. His results were un- 

 varying and definite. The blood serum of his animals never ex- 

 hibited any bactericidal power against the streptococcus, and the 

 attenuated race, like the virulent one, grew well in the serums of 

 the rabbit, dog and guinea-pig. 



More recently, Wallgren 1 has taken up the study of the im- 

 munity and susceptibility of rabbits with respect to the streptococcus. 

 His conclusions are, on the whole, in accord with those of his pre- 

 decessors. He found that if the injected streptococci were not very 

 virulent phagocytosis began immediately after the injection into the 

 peritoneal cavity and continued as long as there were any strepto- 

 cocci to be attacked. In those cases, on the other hand, where the 

 streptococcus was endowed with a greater virulence, a transitory 

 phagocytosis took place at the beginning of the infection ; but the 

 streptococci soon succeeded in adapting themselves to the struggle 

 with the leucocytes and kept them at a distance. The multipli- 

 cation of the streptococci could then go on without restraint and 

 the animal soon succumbed to a generalised infection. Wallgren 

 considers that, in the defence of the organism against the strepto- 

 coccus, the products of the destroyed leucocytes may, sometimes, 

 play a part. 



As the mechanism of natural immunity against the groups of 

 bacteria bacilli, spirilla (and vibrios) and cocci presents a very great 

 analogy in all three, it might be considered superfluous to continue 

 1 Ziegler's Beitr. z.path. Anat., Jena, 1899, Bd. xxv, S. 206. 



