COLLODIONISATION OF SECTIONS. 185 



does not produce a membrane on the paraffin in drying, and 

 therefore has no tendency to cause sections to roll. It has 

 further the advantage that it penetrates to a certain depth 

 below the surface of the preparation, and fixes the deeper 

 layers of it in their places. The collodion must be diluted 

 with ether as soon as it begins to show signs of leaving a shiny 

 surface on the paraffin. 



" Take the brush out of the collodion, wipe it against the neck 

 of the bottle, so as to have it merely moist with collodion, and 

 quickly pass it over the free surface of the preparation. Care 

 must be taken not to let the collodion touch the vertical sur- 

 faces of the paraffin, especially not the one which is turned 

 towards the operator, as that will probably cause the section 

 to become stuck to the edge or under surface of the knife. 

 As soon as the collodion is dry, which ought to be in two or 

 three seconds, cut the section, withdraw the knife, and pass 

 the collodion brush over the newly exposed surface of the 

 paraffin. Whilst this last layer of collodion is drying, take 

 up the section from the knife and place it with the collodion- 

 ised surface downwards on a slide prepared with fixative of 

 Schaellibaum. Then cut the second section, and repeat the 

 manipulations just described in the same order. A skilful 

 operator can cut ribbons of sections, collodionising each 

 section." 



HENKING (Zeit.f. wiss. Mik., iii, 4, 1886, p. 478) objects to 

 the above process that the ether of the collodion softens the 

 paraffin, and proposes a solution of paraffin in absolute 

 alcohol. The solution is made by scraping paraffin into 

 absolute alcohol. 



For extremely brittle objects, such as ova of Phalangida, 

 the same author recommends a thin (light yellow) solution of 

 shellac in absolute alcohol. 



HEIDEE (Embryonalentw. v. Hydrophilus, 1889, p. 12; cf. 

 Zeit. f. wiss. Mik., viii, 4, 1892, p. 509) employs a solution 

 made by mixing a solution of gum mastic in ether, of a 

 syrupy consistency, with an equal volume of collodion, and 

 diluting the mixture with ether until quite thin and liquid. 



283. Clearing and Mounting. The sections having been 

 obtained are generally mounted on a slide in serial order by 

 one of the methods described in the chapter on " Serial Section 



