Special Methods 129 



is oriented in a gelatin matrix on the supporting blocks, cooled until 

 the gelatin sets, and then placed in strong formalin to harden the 

 gelatin. In cutting, flood the knife with water. 



If the material is to be stained, stain it in bulk before putting it 

 into the gelatin, since the gelatin stains very deeply. Of course, 

 the gelatin could be dissolved with hot water, or hot water and acetic 

 acid, but all the advantage of a matrix would be lost. 



It would be worth while to try this method thoroughly with soft, 

 succulent tissues and with hard tissues which become still harder 

 if dehydrated. 



SCHULTZE'S MACERATION METHOD 



Various solutions are used to separate a tissue into its individual 

 cells. These solutions dissolve or weaken the middle lamella so that 

 the cells are easily shaken or teased apart. Schultze used strong nitric 

 acid and potassium chlorate. Put the material, which should be in 

 very small pieces, into a test-tube; pour on just enough nitric acid 

 to cover it, and then add a few crystals of potassium chlorate. Heat 

 gently until bubbles are evolved, and let the reagent act until the 

 material becomes white. Four or five minutes should be sufficient. 

 The fumes are disagreeable and are very injurious to microscopes. 

 Pour the contents of the tube into a dish of water. After the material 

 is thoroughly washed in water, it may be teased with needles and 

 mounted, or it may be put into a bottle of water and shaken until 

 many of the cells become dissociated. 



After a thorough washing in water, the material may be stained. 

 The large tracheids of ferns, dissociated in this way and stained in 

 safranin or methyl green, make beautiful preparations. 



PROTOPLASMIC CONNECTIONS 



In exceptional cases, like the sieve plates of the Cucurbitaceae, 

 the protoplasmic connections show plainly with ordinary methods, 

 but in most cases it is necessary to resort to special methods in order 

 to demonstrate protoplasmic continuity. In these special methods a 

 reagent is used which causes the membranes to swell before the stain 

 is applied. It is only by such an exaggeration that the more delicate 

 connections can be shown. 



