60 PRACTICAL HISTOLOGY. 



cutting, the section has to pass between the spring and the knife> 

 and is thus largely prevented from curling up. 



Curled-up paraffin sections may be made to uncurl by being 

 placed in water at about 40 C. (Gaskell). 



Cutting a Continuous Series of Sections in Celloidin. The 

 tissue, embedded in celloidin, is clamped in a microtome, e.g., that 

 of Jung, and section after section is made. The knife must pass at 

 an acute angle through the celloidin, and must be moistened with 

 80 per cent, alcohol. This is easily effected from a wash-bottle 

 Schanze of Leipzig supplies such a bottle provided with a valve, 

 which facilitates the outflow of a gentle stream of alcohol upon the 

 cutting blade. Weigert's method of arranging and fixing the 

 sections on a slide is the best. Each section in celloidin as it is made 

 is laid upon a narrow strip of curl-paper by means of a camel's-hair 

 pencil. The curl-paper is kept moist by being placed on a plate 

 covered with blotting-paper well moistened with 80 per cent, alcohol. 

 The sections are laid upon the curl-paper in the order desired. 



A slide is coated with a layer of thin collodion, and when it is dry, 

 the celloidin sections on the curl-paper are transferred to it. This 

 is done by lifting up the curl-paper, and placing it, sections lower- 

 most, upon the coating of collodion on the slide. Press on the 

 whole with a piece of dry blotting-paper. The sections adhere to 

 the slide, and the curl-paper is removed. Dry the sections with 

 blotting-paper, and pour over them a layer of thin collodion. They 

 are now permanently fixed, and can be stained on the slide in any 

 way that may be desired. This is an extremely convenient method 

 for serial sections of the central nervous system. 



XL FIXATIVES AND SUBSEQUENT TREATMENT 

 OF SECTIONS. 



Further Treatment of Sections. 



This depends on how the sections have been made, and whether 

 they have or have not been previously stained. Paraffin sections 

 must be freed from paraffin. If they are unstained, they must bo 

 stained. In most cases it is found advantageous to fix paraffin 

 sections to the slide by means of a "fixative." Many sections can 

 thus be fixed on one slide, and treated simultaneously. The series 

 of events will then be for unstained paraffin sections : 



(1.) Fixation on a slide. 



(2.) Removal of paraffin. 



(3.) Staining the section. 



(4.) Mounting the specimen. 



