GENERAL METHODS. 7 



freely evolved. The reagent is then generally allowed to* 

 act for a few minutes until the pieces are quite white, when 

 the whole contents of the test-tube are poured out into a 

 crystallizing dish filled with water. The pieces of macerated 

 tissue are then placed directly, or, better, after washing in 

 pure water, or also in alcohol, upon a glass slide. Here 

 they can be readily separated, by needles or similar means,, 

 into their separate cells. 



Often the isolation of the cells of large pieces of tissue 

 which have been treated with the macerating fluid may be 

 effected by shaking the pieces violently in a glass half full 

 of water. 



It should be remarked that the heating of this macerating^ 

 mixture should preferably be carried on under a hood, or at 

 least not in the neighborhood of a microscope, on account 

 of the evolution of injurious gases. 



2. Chromic Acid (CrO 8 ). Chromic acid is especially use- 

 ful for the isolation of the cells of sections. These are 

 placed in a concentrated aqueous solution of the acid, and, 

 after it has acted for half a minute to five minutes, are 

 washed in a large quantity of water. The sections are usu- 

 ally then readily separated into their cells. Chromic acid 

 attacks the cell-membranes much more strongly, when act- 

 ing longer, than does Schulze's mixture, which is in general 

 preferable, although its manipulation requires somewhat 

 more care. 



3. Caustic Potash. Caustic potash is useful, especially with 

 delicate tissues, such as the roots of Taraxacum officinale. 

 The tissues should be boiled for a few minutes in a solution 

 containing about 50% of potassium hydrate and then placed 

 in water. The cells are then readily isolated by teasing. 

 Dilute caustic potash is also recommended by Solla (I) for 

 the isolation of cork cells. 



4. Glycerine and Sulphuric Acid. According to the 

 method proposed by A. Fischer (IV, p. XCVl), it is possi- 

 ble at the same time to recognize starch in the isolated 

 cells. This author places isolated vascular bundles or suit- 

 able sections in a solution of iodine in glycerine under a 



