Embedding Tissues and Section-Cutting 141 



zinc plate of the microtome, and place the tissue in it. 

 Commence working the bellows, and as soon as all the gum 

 has frozen add some more and freeze again, and so on 

 until the tissue is completely covered and frozen into a solid 

 mass. 



(6) The best instrument for making the sections is the 

 blade of a carpenter's plane. Hold it firmly in the right 

 hand, and work the microtome screw under the machine 

 with the left. Plane off the sections as quickly as possible. 

 They should all collect on the plane iron. If they roll up 

 or fly off, the tissue is frozen too hard, or there is not 

 enough syrup in the gum. If the former is the case, allow 

 the mass to thaw a little ; if the latter, add some more syrup 

 to the gum mixture, and soak the tissue again. 



When the sections are cut, place them in a saucer of 

 water, which must be changed several times until all trace 

 of gum is removed. Water that has been boiled and allowed 

 to cool will remove the gum sooner than cold water. When 

 quite free from gum, the sections may be bottled up in 

 methylated spirit until required for staining. 



Embedding- in Celloidin. Dissolve Schering's celloidin 

 in equal parts of absolute alcohol and ether until the solu- 

 tion is as thick as glycerine. Divide the solution into two 

 parts, to one of which add an equal part of absolute alcohol 

 and ether. Dehydrate the specimen in absolute alcohol 

 for several hours, then transfer to the thinner solution of 

 celloidin, and soak until perfectly saturated ; place in the 

 thick celloidin for about an hour, or until required. Take 

 a cork and paint over one end a layer of celloidin, and let 

 it dry ; this will prevent air bubbles rising from the cork 

 and lodging in the mass. Take the specimen from the 

 celloidin and lay it on the cork, and let it stand for a minute 

 or two, then add some more celloidin until the tissue is 

 completely covered, and set aside, and when the mass has 

 attained such a consistency that on touching it with the 

 linger no impression will remain, place it in 50 per cent, 

 alcohol for an hour or two to complete the hardening, or it 



