10 REAGENTS. 



the hard and soft kinds. The melting point can be lowered by 

 the addition of chloroform. It must be remembered, however, 

 that before any attempt is made to section imbedded tissue, all 

 of the chloroform must be driven off in the infiltrating oven, 

 otherwise the paraffine will be too soft for support. Turpentine 

 can be used in place of the chloroform and is perhaps quite as 

 good. 



Phosphoric Acid. 



Phosphoric acid is sometimes used to remove water from 

 tissues, and when added to any containing crystalloids, it causes 

 the latter to swell. 



Rosalie Acid. 



This acid is used in connection with sodic carbonate as a test 

 for vegetable jelly, staining it red. It is useful in coloring the 

 callosities of sieve-tubes and in bringing out the general structure 

 of cribrose tissue. 



Sugar. 



If tissue containing protoplasm is left for some time in a thick 

 syrup of cane sugar and then transferred to H 2 SO 4 , it will turn 

 a red color. The reaction is not always a certain one. A 10 per 

 cent, solution of sugar is very useful for pollen and for spore cul- 

 tures. 



Sulphuric Acid. 



Sulphuric acid is used in connection with many tests 

 and is also valuable in breaking down cellulose walls, without 

 shrinking the protoplasm. This makes it especially important in 

 demonstrating the continuity of protoplasm. It is also used in 

 connection with iodine to determine the purity of the cellulose that 

 makes up the cell walls of any tissue. In this test the tissue is 

 first treated with a tincture of iodine, and sulphuric acid is then 

 added. The walls will turn blue if they are composed of pure 

 cellulose. Dilute sulphuric acid causes starch grains to swell, 

 while with the concentrated acid they are dissolved. Pure cellulose 

 walls are likewise dissolved by the acid, while cutinized ones resist 

 its action. Fat bodies are not soluble in it, but they form small 

 refrative drops. 



