Preparing Vegetable and Animal Tissues. 433 



Method B — continued. 



strong diffusion currents will be set up and 

 the protoplasmic contents of the cell separate 

 from the cell-wall. 



2. Pour off the fluid till the tissue is just covered, 



and add absolute alcohol up to the original 

 bulk. Move about the bottle gently every 

 three or four hours. Most of the picro-cor- 

 rosive material will thus be extracted after 

 twenty-four hours. 



3. Draw the fluid rapidly off by means of a pipette, 



and add absolute alcohol up to half of the 

 original bulk. Any drying of the tissue must 

 be carefully guarded against. Leave for twenty- 

 four hours, and repeat the process. 



C. The replacement of the alcohol by chloroform. 



1. Pass, by means of a pipette, the chloroform- 



alcohol mixture to the bottom of the vessel, 

 when the tissue will float on the mixture. 

 Remove then the superfluous alcohol by a 

 pipette, leaving only enough to cover the tissue. 



2. Wlien the tissue has sunk in the chloroform- 



alcohol mixture, introduce by a pipette pure 

 chloroform, on which the tissue will float ; the 

 fluid above the tissue is removed by a pipette. 

 After twenty-four hours the tissue may or may 

 not have sunk in the chloroform ; if not, it 

 may be induced to do so by heating the chloro- 

 form to 20° C. (not higher) ; if this fail, a little 

 sulphuric ether may be added. After the tissue 

 has sunk, leave for twenty-four hours. 



3. Place a fresh supply of chloroform at the bottom 



of the vessel (50 times the bulk of the tissue), and 

 if there is a distinct line of demarcation between 

 the newly-added and the old chloroform, the 

 upper layer should be removed by a pipette. 



D. The replacement of chloroform by paraffin. 



1. Place the tissue in a warm chamber heated to 

 25° C; add solid paraffin in pieces up to the 

 size of a small pea. After each piece has dis- 

 solved, the bottle has to be moved about very 



TRANS. BOT. SOC. VOL XVIII. 2 T 



