278 A MANUAL OF BACTERIOLOGY 



by saturation with ammonium sulphate but not with 

 magnesium sulphate, and hence is neither a peptone nor 

 a globulin, contains a large amount of sulphur, and gives 

 the biuret and Millon's tests. A curious property of this 

 substance is that small quantities (2'5 mgrm. per kilo- 

 gramme of the body-weight) do not produce their effects 

 until the lapse of weeks. Brieger and Boer in a later 

 research prepared the diphtheria tox-albumin by precipi- 

 tating a bouillon culture with a 1 per cent, solution of 

 zinc sulphate or chloride. The precipitate of the zinc 

 double salt was washed with slightly alkaline water and 

 decomposed with a stream of carbonic acid gas. The 

 purified tox-albumin gives the xanthoproteic, biuret, and 

 Adamkiewicz's reactions, and the red coloration on heating 

 with Millon's reagent. 



According to Ehrlich the toxin broth is a complex 

 mixture of toxic constituents belonging to the proteins, 

 but this is denied by Madsen and Arrhenius (see p. 165). 

 Its poisonous property gradually diminishes on keeping, 

 and is destroyed by boiling in five minutes, at lower 

 temperatures more slowly, and also by light. 



Diphtheria antitoxin. By the injection of sub-lethal 

 and increasing doses of the toxin into an animal an anti- 

 toxin is generated. For the preparation of a potent 

 antitoxin for therapeutic use the first essential is a highly 

 toxic toxin, and for obtaining this a diphtheria bacillus of 

 high virulence is required, and few strains possess the 

 necessary virulence. The virulent bacillus is grown in an 

 alkaline broth (rendered alkaline to the extent of about 

 5*7 c.c. of normal caustic soda solution per litre beyond 

 the neutral point of litmus) in Erlenmeyer flasks containing 

 half to one litre for eight to twelve days at 37 C. Various 

 small details have to be attended to in order to obtain toxin 

 of maximum toxicity ; it is important that growth should 

 occur upon the surface of the broth. The use of meat some 



