CELLO I DIN 107 



is no further room on the knife, the sections can be transferred to 

 a vessel containing 70 per cent, alcohol or placed in series on strips 

 of thin paper moistened with alcohol. It will be found more 

 convenient to continue cutting the sections as quickly as possible 

 and not to hesitate too long between each section. Undue 

 evaporation of alcohol from the block may lead to slight shrinkage 

 and to sections of uneven thickness. 



(b) Dry cutting method. Celloidin blocks infiltrated with 

 cedarwood oil or a similar clearing fluid may be cut with a dry 

 knife. Walls {Stain Tech., xi, 1936, p. 89) describes a method for 

 cutting dry celloidin sections with a rotary microtome. Some 

 workers prefer to cut paraffin infiltrated blocks with a dry knife 

 but it is doubtful whether very thin sections can be obtained so 

 easily as with the wet method. 



195. Preparation of Sections for Staining and Mounting. If 

 sections are to be stained but not kept in serial order, it is usually 

 more convenient to handle them separately and leave the final 

 mounting until after dehydration and clearing. Sections containing 

 paraftln wax must first be dehydrated with absolute alcohol 

 containing 25 per cent., or more, of chloroform and transferred to 

 xylol or benzol to remove the wax ; then returned to the absolute 

 alcohol-chloroform and through graded alcohols to water for 

 staining. Small sections can be handled very conveniently if the 

 solutions are placed in small china egg-cups or in small glass 

 staining dishes. Large sections need more careful handling. The 

 method of attaching sections in series to the outer surface of a 

 cylindrical glass bottle by means of rubber bands is to be recom- 

 mended, see Hallpike (Journ. Path, and Bact., xxxviii, 1934, 

 p. 247). The bottle holding three or four circumferential rows 

 of sections can be then immersed on end in glass vessels of 

 slightly larger diameter, containing the staining solutions. 



196. Tissues imbedded in celloidin generally show increased 

 affinity for dyes and it will be necessary in many cases to 

 modify the staining techniques originally devised for paraffin 

 sections. Very weak solutions of nuclear dyes, such as Ehrlich's 

 hsematoxylin, give sharper staining than the full strength 

 solutions, e.g. : — 



Ehrlich's haematoxylin . 0-25 c.c. 

 Dist. water . . .50 c.c. 



Stain for several hours or overnight. 



The common criticism that even thin celloidin sections lack the 

 sharp resolution of paraffin sections, is often due to misuse of the 

 staining solutions. 



After staining, the sections are dehydrated with the absolute 

 alcohol-chloroform and transferred to a clearing agent which will 

 soften the celloidin without actually dissolving it. Xylol, toluol 

 and benzol harden the celloidin and prevent even flattening in 



