Production of Sections 267 



point previously determined upon, in which it is kept from 

 an hour or so to several days. The length of time required 

 for the final infiltrating process must be found by experience, 

 as it varies greatly in the different objects suitable for 

 microtomic analysis. The principle to be aimed at is the 

 complete infiltration of the entire substance by the paraffin 

 and the elimination of all air and clearing medium. If 

 any of the two latter substances remain in the object when 

 the embedding is complete, all attempts at securing a good 

 range of sections are hopeless. All your cunning at knife- 

 grinding, all your skill and delicacy of manipulation with 

 the microtome, will count as nothing in the impossible 

 task of obtaining a good series of sections from imperfectly 

 infiltrated objects. We may mention that hard objects of 

 a dense nature take much longer to infiltrate than delicate 

 structures of a more open character. Again, some objects 

 may be covered with skin of such dense texture as to defy 

 the entry of the wax* ; portions of such skin must be 

 removed or slits made through it either previously to 

 fixing or before the paraffin-bath. 



We have above indicated the method by which objects 

 may be fixed, hardened, and passed into paraffin, in which 

 they are perfectly preserved being, in fact, embalmed. 

 By this process almost any object may be preserved for 

 years without danger of deterioration to any of its elements, 

 provided always that the wax is kept perfectly dry and cool. 

 It is not, however, always convenient to embed at once 

 immediately after the fixing; consequently, a method must 

 be sought for preserving the object in another way. After 

 fixation and hardening of the tissues in the usual way, 

 most subjects may be preserved indefinitely in the following 

 mixture : 



90 per cent, alcohol ... 100 c.c. 



Pure glycerine ... 100 ,, 



Distilled water ... 100 ,, 

 Glacial acetic acid 1 , 



Preserving fluid. 



Hearson's vacuum oven is useful in such cases. 



