22 



Chapter I 



are in general very resistant to anthrax 1 . Under analogous conditions 

 the streptococci which, as a rule, do not produce a mucous sheath, 

 will develop one of exceptional size. The guinea-pig is in general 

 very resistant to the streptococcus against which it exhibits a very 

 effective reaction. Sometimes, however, this immunity gives way ; 

 in such instances, as demonstrated by J. Bordet 2 , the streptococcus, in 

 order to overcome the natural resistance of the guinea-pig, is found 

 to have surrounded itself with a sheath of a thickness such as is 

 seldom to be met with in the world of bacteria (Fig. 2). 



Fig. 2. Streptococcus surrounded 

 by a protective envelope. 



Fig. 3. Tubercle bacillus surrounded 

 by a transparent envelope and en- 

 closed in the giant cell oi a gerbil. 



Analogous facts are also observed in cases where the micro- 

 [25] organism is defending itself against the action of substances enclosed 

 in animal cells. I may cite as an example the tubercle bacillus in 

 the interior of the giant cells of a gerbil (Meriones shawii), where, 

 under the influence of noxious substances contained in these cells, the 

 tubercle bacillus (Fig. 3) envelops itself in a transparent sheath 

 similar to that of the bacillus or of the streptococcus. As the action 

 of the giant cell still does not cease, the tubercle bacillus secretes 

 a second sheath (Fig. 4) and continues to surround itself with 



1 Metchnikoff, Virchow's Archiv, 1884, Bd. xcvn, S. 510. 



2 " Contribution a 1'etude du serum antistreptococcique," Ann. de I'Inst. Pasteur, 

 Paris, 1897, t. xi, p. 177, Planche V. 



