VITAL PHENOMENA OF BACTERIA. 71 
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 ptomain. The 
alcohol is evaporated by heat, the mercury separated 
by sulphuretted hydrogen, and a double compound 
formed with gold and platinum, the crystallizability 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 ptomains, 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. BacreriAL 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 ; 
