42 Paraffin Melhod (chap. ?,) 



10. Transfer to melted paraffin #2: | to hour. 



11. Embed. 



If the tissue is well hardened by the fixative, it is not necessary to 

 dehydrate the tissue through a number of graduated steps, such as 50, 

 60, 70, 80, 95% and absolute alcohol. Even the elimination of the 50% 

 and 00% steps is possible when time presents a problem; also the use of 

 isopropyl alcohol materially shortens the schedule. 



In passing tissues from one fluid to another, use the decantation 

 method. This avoids excessive manipulation with forceps and reduces 

 injury to the tissue. After pouring off a solution, drain the tissue bottle 

 briefly against a paper towel or cleansing tissue to pull off as much as 

 possible of the discarded solution. This reduces contamination of the 

 new solution. Since 95% alcohol, absolute alcohol, clearers and melted 

 paraffin all contribute to the hardening of the tissue, avoid leaving it 

 in any of these fluids for longer than the maximum time (preferably 

 leave only for the minimum period), and never overnight. Effective 

 infiltration takes place only when the paraffin is actually melted. Partly 

 melted, "mushy" paraffin penetrates poorly, if at all. 



Automatic Tissue Processors 



Most large laboratories now handle the foregoing processes by ma- 

 chine; the changes are controlled with a timing device, and the tissues 

 are shifted automatically through a series of beakers or other type of 

 container. The timing device can be set on a schedule to handle the 

 changes during the night in order that the tissues will be ready for 

 embedding when the technician arrives at the laboratory in the morn- 

 ing. Small metal or plastic receptacles with snap-on lids hold the tissues 

 and labels, and are deposited in a basket which clips into the bottom of 

 the lid of the instrument. When the time arrives for removal of the 

 tissues to a new solution, the lid rises and rotates to lower the basket 

 into the next container. The two final beakers are thermostatically con- 

 trolled paraffin baths. The technician can set the timing device for any 

 interval desired — 15 minutes, 30 minutes, I or more hours, etc. — over 

 a period of 24 hours. The newest models have a clock which can control 

 the instrument over a week end or several days. (The above description 

 applies to the Autotechnicon of Technicon Company.) 



There are several tissue processors on the market; in addition to the 

 Autotechriicon, there is a Lipshaw model, and the Tissuematon of the 

 Fisher Scientific Company. Complete operational directions are sup- 

 plied with all models. 



