182 IMBEDDING METHODS. 



the rolling. To this end, the block of paraffin is pared to the 

 shape of a wedge five or six times as long as broad, the object 

 being contained in the head or broad part, and the edge 

 turned towards the knife. The sections are allowed to roll 

 and come off as coils, the section of the object lying in the 

 outermost coil, which will be found to be a very open one 

 indeed, very nearly flat. Lay the coil on a slide with this end 

 downwards, warm gently, and the part containing the object 

 will unroll completely and lie quite flat. 



The most efficacious plan for unrolling sections is perhaps 

 the combined treatment with fluid and heat ((TASKELL, Quart. 

 Journ. Mic. Sci., xxxi, 1890, p. 382; M. DUVAL, Journ. de 

 VAnat. et de la PhysioL, 1891, p. 26; HENNEGUY, ibid., 1891, 

 p. 398 ; GULLAND, Journ. of Anat. and PhysioL, 1891, p. 56 ; 

 and others) . The rolled sections are either floated on to the 

 surface of warm water or warm alcohol contained in a watch- 

 glass or suitable dish, which causes them to flatten out, and 

 are then transferred to a slide to be mounted in any desired 

 manner. Or the slide has a layer of water spread over it, 

 the sections are laid on the water, and the slide is heated (to 

 about 45 to 50 C.) until the sections flatten out, which 

 happens in a few instants. The method can be made avail- 

 able for fixing series of sections to the slide ; the further 

 details necessary for the successful accomplishment of this 

 are given in Chap. XVII, 324. 



Minute examination of paraffin sections sometimes reveals 

 certain distortions and dislocations or even ruptures of delicate 

 elements. I have often noticed that in certain regions of my 

 sections all the karyokinetic figures are drawn up to one side 

 (always the same side) of the nucleus, leaving the rest of the 

 nucleus empty and vacuolar in appearance. The achromatic 

 fibrils of the division spindle are frequently ruptured, and I 

 have not rarely found isolated chromosomes lying far from 

 the nucleus in the body of cells, or even outside the cells 

 themselves. These phenomena have generally been ascribed 

 to " shrinkage " caused by the action of the fixing agents or 

 the processes of dehydration or imbedding. HEIDENHAIN 

 (Ueber Kern u. Protoplasma, inFestschr. Herrn Geheimr. A. v.. 

 Kolliker gewidm., 1892 ; see Zeit. f. wiss. Mik., ix, 2, 1892, 

 p. 200) thinks that they are often caused by excessive tilt of 

 the under surface of the microtome knife. If this be found 



