212 CLINICAL BACTERIOLOGY. 



taining the bacteria is under positive pressure, or Kitasato's 

 porcelain cylinders in which suction of the filtrate takes 

 place). Instead of filtering them, the bacilli in the culture 

 may be destroyed by addition of carbolic acid in propor- 

 tion of 0.5 per cent. 



Reference has been made to the efforts directed to 

 obtaining the poison chemically pure from the toxin-con- 

 taining bouillon-filtrate (p. 29). Brieger and Boer have 

 made the greatest advances in the preparation of the diph- 

 theria-toxin. To the toxin-containing filtrate they add twice 

 as much of a one per cent, solution of zinc chlorid. The 

 resulting precipitate is agitated with from a three to a six 

 per cent, solution of ammonium carbonate, and enough 

 ammonium phosphate is added to effect complete solution ; 

 then a delicate white turbidity results on addition of zinc 

 phosphate. To free the solution of metallic precipitate, it 

 is passed through a hardened filter, is well washed, and the 

 filtrate is saturated with ammonium sulphate. In this way 

 a precipitate is obtained that contains the diphtheria-toxin. 

 A portion of the peptone adherent to the toxin is separated 

 by solution in water and precipitation with sodium sulphate, 

 but the albumin can not be completely eliminated, even by 

 repeated washings. 



Brieger and Boer have, therefore, cultivated the diph- 

 theria-bacillus upon dialyzed urine of human beings, and 

 have prepared from this albumin-free culture-medium by 

 the methods just described a toxin free from peptone 

 and albumin. This toxin is destructive to animals, and 

 the conditions found after death are characteristic. It 

 does not yield the usual reactions of albumin, and is unin- 

 fluenced by reducing substances, but it is almost immedi- 

 ately destroyed by oxidizing substances. Acids also de- 

 stroy the purified toxin of Brieger and Boer, while feeble 

 alkalies do not. 



By means of a concentrated solution of ammonium 

 chlorid it is possible, as Brieger and Boer, further, have 

 shown, to free the bodies of the bacteria completely of the 

 specific poison. If the bacteria thus treated are ground to 

 powder, and small amounts of this suspended in water are 

 injected into guinea-pigs, the animals die with necrosis and 

 suppuration at* the point of infection. The bodies of the 

 bacilli are, therefore, possessed, further, of a necrotic 

 poison. 



