VITAL PHENOMENA OF BACTERIA. 7] 



sistency. This is then dissolved in 96 per cent, alcohol, 

 freed from albumin and other contamination by an 

 alcoholic solution of lead acetate, the lead precipitated, 

 the filtrate concentrated, and again precipitated by an 

 alcoholic solution of mercuric chloride, which forms a 

 double mercury compound with the ptomai'n. The 

 alcohol is evaporated by heat, the mercury separated 

 by sulphuretted hydrogen, and a double compound 

 formed with gold and platinum, the crystal lizability of 

 which permits of its purification; or the crystalline hydro- 

 chloride is directly obtained, and the free bases, which 

 are often liquid, separated by means of sodium hydrate. 



Many of these ptomai'ns, like most vegetable alka- 

 loids when they are are set free by sodium or potassium 

 hydrate, are obtainable by agitation with ether in aque- 

 ous solution; but Brieger's method is preferable, because 

 many substances not taken up by ether are here ex- 

 tracted. 



Complex Albuminoid Poisons Toxalbumins or Toxins. 

 These may be divided into two classes: 



1. BACTERIAL PROTEINS (Buchner). By these are 

 understood poisonous substances of a proteid nature 

 produced by bacteria which are not affected by heat, 

 which are capable of producing fever (pyogenic) and 

 causing inflammation (phlogogenic), and which can be 

 obtained by boiling for several hours potato cultures 

 treated with an 0.5 per cent, solution of potassium 

 hydrate (about 50 volumes of potassium hydrate to 1 

 volume of bacterial substance). From the clear, fil- 

 tered liquid the proteins are precipitated by weak acid, 

 carefully added, and the precipitate washed and dried; 

 before use they can be dissolved in weak soda solution. 



The best known protein is Koch's old tuberculin; 



