162 



BACTERIAL POISONS. 



of which carries two small glass tubes. One of these, B, 

 extends to the bottom of the flask, while a terminates just 

 above the surface of the liquid. The tube, A, is connected 

 with a water-pump or aspirator, which draws the vapor 

 through the tube. In order to prevent the return of con- 

 densed fluids, the end of A in the flask is curved upon 

 itself The tube, b, is finely drawn out and through it a 

 current of air is constantly moving. This prevents the 

 formation of a deposit or a pellicle in the fluid. By regu- 



lating the amount of air coming through this tube, more 

 or less of a vacuum will be formed in the flask. After 

 evaporation to a syrup, au extraction is made with 96 per 

 cent, alcohol, and the filtered extract is treated with a warm 

 alcoholic solution of lead acetate. The lead precipitate is 

 removed by filtration, the filtrate evaporated to a syrup and 

 again extracted with 96 per cent, alcohol. The alcohol is 

 driven off; the- residue taken up with water; traces of 

 lead removed with hydrogen sulphide ; and the filtrate, 

 acidified with hydrochloric acid, evaporated to a syrup. 

 This syrup is extracted with alcohol, and the filtrate pre- 



