184 IMBEDDING METHODS. 



microtome or Strasser's ribbon microtome. The Thoma 

 microtome well flooded with oil is sufficient. But the au- 

 tomatic microtomes are certainly most advantageous for 

 this purpose, and amongst them the Cambridge Rocking 

 Microtome, and the Minot, may be quoted as giving admi- 

 rable results. 



Various plans, such as coating the edges of the paraffin 

 with softer paraffin, or with Canada balsam, or the employ- 

 ment of specially prepared paraffin, have been recommended, 

 with the idea that they help the sections to stick. None of 

 these devices is necessary. For the prepared paraffin of Spee, 

 Brass, and Foettinger, see below, 286. 



282. Collodionisation of Sections. Some objects are by nature 

 so brittle that, notwithstanding all precautions taken in 

 imbedding and previous preparation, they break or crumble 

 before the knife, or furnish sections so friable that it is im- 

 possible to mount them in the ordinary way without some 

 impairment of their integrity. Ova are frequently in this 

 case. The remedy for this state of things consists in cover- 

 ing the exposed surface of the object just before cutting each 

 section with a thin layer of collodion, which serves to hold 

 together the loose parts of even the most fragile sections in 

 a wonderfully efficacious way ; and the same treatment applied 

 to tissues which are not specially fragile will enable the ope- 

 rator to cut sections considerably thinner than can be obtained 

 in the usual way. BUTSCHLI has obtained in this manner 

 sections of less than I fi in thickness. 



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 this 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. 



MARK (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 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 



