30 HISTOLOGY OF MEDICINAL PLANTS 
that they did in the living plant, and to fix the parts so killed. 
After the fixing process is complete, the specimen is freed 
of the fixing agent by washing in water. From the water-bath 
the specimens are transferred successively to 10, 20, 40, 60, 70, 
80, go, and finally roo per cent alcohol. In this 100 per cent 
alcohol-bath the last traces of moisture are removed. The 
Fic. 31.—Paraffin-embedding Oven 
length of time required to leave the specimens in the different 
percentages of alcohols varies from a few minutes to twenty- 
four hours, depending upon the size and the nature of the 
specimen. 
After dehydration the specimen is placed in a clearing agent 
—chloroform or xylol—both of which are suitable when em- 
bedding in paraffin. The clearing agents replace the alcohol in 
the cells, and at the same time render the tissues transparent. 
From the clearing agent the specimen is placed in a weak solu- 
tion of paraffin, dissolved xylol, or chloroform. The strength of 
the paraffin solution is gradually increased until it consists 
of pure paraffin. The temperature of the paraffin-embedding 
