150 IMBEDDING METHODS. 



collodion on the free surface of each section just before cutting 

 it. But this practice has two defects; the quantity of col- 

 lodion employed sensibly softens the paraffin ; and the thick 

 layer of collodion when dry causes the sections to roll. 



MAKE (Amer. Natural., 1885, p. 628 ; cf. Journ. Roy. Mic. 

 Soc., 1885, p. 738) gives the following directions : 



Have ready a little very fluid collodion in a small bottle, 

 through the cork of which passes a small camel-hair brush, 

 which just dips 'into the collodion with its tip. The collodion 

 should be of such a consistency than when applied in a thin 

 layer to a surface of paraffin it dries in two or three seconds 

 without leaving a shiny surface. Collodion of this consistency 

 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 surfaces 

 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 collodionised 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 sec- 

 tions, 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 abso- 

 lute alcohol. 



For extremely brittle objects, such as ova of Phalangida, 



