TOXINES. 1 1 



death or injury of the cell protoplasm, or, as in the case of 

 zymase, after breaking down the cell wall ; and we also know 

 that Monilia Candida will not give up its invertase to the 

 surrounding medium, under any conditions whatsoever. 



When toxine solutions have once been obtained by nitration 

 of the cultures, or analogous preliminary means, such as extrac- 

 tion of seeds, &c., they can at once be used, although containing 

 numerous impurities, for physiological experiments. Moreover, 

 even in this impure condition some rough experiments can be 

 made with them to determine the behaviour of the respective 

 toxines towards physical and chemical agents. 



Moreover, in order to have it in a more suitable form for 

 keeping, this solution may also be concentrated with various 

 precautions, or may even be evaporated to dryness without 

 materially injuring the toxine. The main conditions are that 

 the temperature must never exceed 45 C. (whence it is best to 

 carry out the evaporation in vacuo), and that any strong acids or 

 bases that may be present must be partially neutralised. 



For a closer investigation of toxines, however, tedious processes 

 of purification are necessary to remove all impurities as com- 

 pletely as possible. The simplest method is dialysis, which, 

 however, only separates the toxine from the salts and peptones 

 also present in the solution, but does not eliminate the proteids. 



Hence, complicated methods have had to be devised to isolate 

 the toxines in the purest possible condition. The favourite 

 methods employed consist of precipitation by means of am- 

 monium or magnesium sulphate with subsequent dialysis, and 

 of precipitation by means of the salts of heavy metals with 

 subsequent decomposition of the resulting double compounds. 

 The first of these methods yields, eventually, only solid concen- 

 trated preparations of toxines which are still impure, although 

 capable of being used for practical purposes, and the second 

 method is the only one that gives approximately pure toxine 

 preparations. A fuller account of its details, which have been 

 worked out, notably by BRIEGER and his pupils, is given in the 

 special part. They include exceedingly tedious manipulations 

 requiring close attention, and consisting, in the main, of precipi- 

 tation with zinc, lead, or mercury salts. The double compounds 

 of the toxines with these salts that are precipitated are again 

 decomposed by means of hydrogen sulphide, or of alkali carbon- 

 ates, or phosphates. Then by means of filtration or dialysis 

 solutions are obtained, which on evaporation in vacuo yield 

 preparations which in favourable cases are very rich in toxine. 

 They invariably, however, still contain considerable quantities 



