IMBKDDJNG MKTHODS (PARAFFIN). Ill 



The primitive form of the process was to place a drop of 

 collodion on the free surface of each section just before 

 cutting it. But tkis practice has two defects ; the quantity 

 of collodion 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. Jonrn. ti^y. 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 that 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 puss 

 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. iciss. Mik., iii, 4, 1886, p. -178) objects to 

 the above process that the ether of the collodion softens the 

 paraffin, and proposes a solution of i>aroffin. in absolute alcohol. 

 The solution is made by scraping paraffin into absolute alcohol. 



