PARAFFIN SECTIONS 107 



twenty hours. It is then embedded by pouring a little 

 of the melted paraffin into a watch-glass, or into a small 

 box formed of folded paper or lead-foil, or by bringing 

 together two L-shaped pieces of brass on a glass plate 

 so that a rectangular cavity is produced. The pieces of 

 tissue are then taken out with a small warmed forceps 

 or needle, adjusted to the position they are required to 

 occupy, and more melted paraffin is poured in, so as to 

 cover them. When a film of solid paraffin has formed, 

 the whole is immersed in cold water so as to cool it 

 rapidly. 



A new paraffin is frequently crystalline in structure, 

 and acts much better after it has been kept melted for 

 some weeks, or is much improved by heating nearly to 

 its boiling-point for five or six days (P. T. Beale). The 

 xylol for clearing may be used several times and the 

 paraffin repeatedly, the remains of old tissues being 

 removed. The time which the tissues require to remain 

 in the alcohol, xylol, and paraffin depends upon their 

 size ; very small pieces may be treated in an hour or 

 two, large ones may require 12-18 hours. 



Other clearing agents, such as chloroform, turpentine, 

 and cedar oil, may be used instead of xylol. The paraffin 

 method is usually straightforward, but small pieces of 

 tissue must not be left too long either in absolute alcohol 

 or in the paraffin bath, for they are liable to become too 

 hard to cut. Thyroid tissue and skin are also rather 

 troublesome ; they become very hard unless the whole 

 process is carried out as rapidly as possible. If the 

 pieces of tissue be large, the capsule of melted paraffin 

 containing the tissue may be placed under the receiver 

 of an air-pump, which is then exhausted. This causes 

 the paraffin to penetrate better, and the process may 

 be repeated two or three times during the period of 

 infiltration. A special form of paraffin oven, devised 



