EMBEDDING, 47 



In cutting sections embedded in celloidin, the knife must be so 

 placed as to cut with as much of the blade as possible. The 

 hardened celloidin is fixed to a piece of cork, which is clamped in 

 the microtome. 



If, however, it be desired to cut sections embedded in celloidin 

 by the freezing method, the following procedure must be adopted. 

 After the tissue embedded in celloidin has been hardened in alcohol, 

 whereby it becomes not only " hardened " but somewhat milky in 

 appearance, the alcohol must be got rid of, which is done by 

 keeping it in running water for twenty-four hours, when it is 

 transferred to a freezing mixture of gum and syrup (p. 49). This 

 freezing fluid gradually penetrates the cheesy-like mass, and dis- 

 places the water. Such a preparation can be frozen in an ordinary 

 microtome. 



For embedding and cutting in celloidin, the following are the 

 stages : 



(1.) Organ hardened, either at first or subsequently, in absolute 



alcohol. 

 (2.) Then in a mixture of equal parts of absolute alcohol and 



ether (1-2 days). 



(3.) In dilute celloidin mixture (1-5 days). 

 (4.) In thick celloidin mixture (1-5 days). 

 (5.) Object placed on cork and exposed to air to dry. 

 (6.) Then in 80 per cent, spirit (i day). 

 (7.) Cut sections. 

 (8.) Stain and \vash them. 

 "(9.) Dehydrate them in 96 per cent, alcohol (and perhaps 1-2 



minutes in absolute alcohol). 



(10.) Clarify with origanum oil, xylol, cedar orbergamot oil. 

 (11.) Mount in balsam. 



Suppose a piece of the human spinal cord is to be embedded in 

 celloidin. After being hardened properly it is transferred from 

 absolute alcohol to ether, for not more than twenty-four hours. It 

 is then placed for 6-8 days in solution of celloidin (3), in solution 

 (2) four or live days and in solution (1) two or three days. It is 

 then embedded in celloidin as described above, and when it begins 

 to harden by evaporation of the ether and alcohol it is transferred 

 to 80 per cent, alcohol for three or four days, which finally hardens 

 it, but it must be completely covered with spirit. If it is to be 

 preserved for some time before it is cut, keep it in 70 per cent, 

 alcohol. 



Sections of an organ embedded in celloidin may also be clarified 

 by means of creosote, or a mixture of i part of creosote and 3 of 

 xylol, which, however, must be quite water-free. 



