MICROINCINERATION 143 



system. A rack running through the tube and extending from both 

 ends serves to support the quartz slabs as they are moved along. 

 Further details of the apparatus have not appeared. 



3. Scott Incineration Procedure 



Scott (1937) gave the following directions for incineration: 



1. Gradually bring to 200° over 10 min. 



2. Gradually elevate to 280° over the next 5 min. 



3. Gradually elevate to 385° over the next 5 min. 



4. Gradually elevate to 480° over the next 5 min. 



5. Gradually elevate to 580° over the next 5 min. 



6. Gradually elevate to 650° over the next 3-5 min. 



7. Shut off furnace and let cool for 5-10 min. 



8. Remove slides from furnace and place cover slip over section 

 as soon as cool enough to handle. Seal edges with a mixture of 1 part 

 paraffin, 1 part beeswax, and 1 part resin (by weight). The use of a 

 cover slip permits observation with an oil immersion objective, and 

 it prevents absorption of moisture and efflorescence of the ash. 

 Greatest care is advised to avoid any air current between the time 

 of removal from the furnace and sealing the cover slip, since the 

 ash is easily disarranged. 



The practice of covering the ash with collodion or Canada balsam 

 is undesirable, since it involves the danger of disarrangement and 

 disturbance of optical properties. 



Variation in the above procedure may be necessary for particular 

 tissues. The greatest shrinkage occurs between 60-70°, and especially 

 in tissues rich in elastic and fibrous material such as blood vessels. 

 In order to produce practically all of the shrinkage in advance, 

 Policard and Ravaut ( 1927) place fixed tissues in absolute alcohol 

 and bring slowly to the boiling point. However, this procedure is 

 not advised by Scott for cytological studies because there is the 

 possibility of dissolving salts. 



The passage of a stream of nitrogen through the tube during 

 incineration was recommended by Schultz-Brauns (1929), and 

 Tschopp (1929) suggested a similar use of oxygen. Policard (1933b) 

 employed nitrogen containing a small concentration of oxygen, which 

 he claimed effects more rapid oxidation. Although satisfactory 

 results have been obtained with these methods, and they seem to 



