388 ADDITIONS. 



placed in a stream of water for some hours to re- 

 move the mercuric salt, and further hardened in 

 alcohol. As the mercuric salt is soluble in alcohol, 

 the tissue may be removed from mercuric chloride 

 to alcohol. In this case, however, the alcohol should 

 be renewed several times. 



Plemming's mixture is used chiefly to harden tissues 

 in which it is desired to make dividing nuclei 

 obvious, and consists of 



Chromic acid 1 p.c. — 15 parts. 



Osmic acid 2 p.c. — 4 parts. 



Glacial acetic acid — ^ to 1 part. 

 In this the tissue should be left two or three days, 

 washed with water, and treated in the usual way 

 with alcohol. 



Imbedding, Section Cutting, Mounting. 



When a number of sections have to be prepared for 

 distribution amongst students, the freezing method 

 given in the Appendix is only satisfactory with 

 tissues that, are firm and hold well together. Other, 

 tissues should be either imbedded in celloidin, or 

 imbedded in hard paraffin with a view to preparing 

 ribbons of sections. 



Paraffin. Ribbons of Sections. 



Imbedding and cutting. The piece of hardened and 

 stained tissue is placed in absolute alcohol for 1 to 

 24 hours. From this it is removed to either chloro- 

 form, turpentine, or oil of cloves. It is then placed 

 in hard paraffin (nielting-point about 58' C), kept at 

 a constant temperature, not greater than 60° C., for 

 two or more hours, and imbedded in the manner 



