SECTIONED MATERIAL. 211 



for several days, they should be left in a 70 percent or 80 

 percent alcoholic medium. 



Sectioned Material. — In a few cases sectioned material may 

 be distributed to the class. Be sure that the slide on which you 

 intend mounting the sections is thoroughly clean. Remove any 

 greasy substance with 95 percent alcohol. On a cleaned slide, 

 smear a very little albumen fixative with your finger-tip and re- 

 move all except the thinnest film. Now place the sections on the 

 albumen over an area the size of the cover-glass to be used, and 

 press them down flat with the tip of a clean, dry finger.^ Warm 

 the slide over an alcohol lamp very carefully until the paraffin 

 in which the sections are embedded is just melted. While the 

 paraffin is still melted treat it with xylol (a jar containing xylol 

 for this purpose is desirable). This will dissolve the paraffin and 

 leave the sections alone adhering to the slide. When the paraf- 

 fin is completely dissolved (this will take but a few seconds), 

 drain off the xylol, apply a drop of balsam, and cover as in total 

 mounts. The preparation is now ready for use, and is per- 

 manent, but must be handled carefully while fresh. 



Application of above directions in the case of a hydroid : 



Hot corrosive, fifteen seconds. 



Cold corrosive, five minutes. 



Water or alcohol, four changes, three or four minutes 



each. 

 Thirty-five percent, 50 percent, and 70 percent alcohol, 



five minutes each. 

 Seventy percent alcohol plus iodin, as in directions above. 



One-half of your material may now be placed in borax-carmine. 

 Leave the material in this till objiects have taken on a good color. 

 (Ask an instructor about this.) When sufficiently stained, put 



^If the sections are not needed for study for a day or more, they may 

 be floated out on water placed over the film of albumen. Heat the water 

 until the sections stretch out flat, but do not melt the paraffin. In not 

 less than twelve hours after the slide is thoroughly dry, it may be trejited 

 as directed in the other case. The value of this method is that it gives 

 perfectly flat sections. 



