KM BEDDING. 4! 



being cut, and the other interstitial embedding, where the sub- 

 stance used for the embedding process is made to penetrate into 

 the interstices of the tissue. 



A. Simple Embedding. 1. The tissue may be clamped between 

 two pieces of carrot, scooped out to receive it, or in elder pith, or 

 (what is very convenient) between two pieces of amyloid or waxy 

 liver hardened in alcohol. 



2. Paraffin. It is sometimes desirable to surround the tissue 

 with paraffin or some such medium. The embedding medium 

 should be about the same degree of hardness as the tissue. 



Two paraffins are required, a hard paraffin melting at 60 and a 

 soft one at 45 C. For use they may be mixed as follows : 



T / Hard paraffin I part 



\ Soft paraffin . . . I ,, 



rj ( Hard paraffin . . . i ,, 



' \ Soft paraffin .... 2 parts. 



Two parts of the hard paraffin and one of the soft yield a mixture 

 which cuts well when the temperature of the room is 21 C. 

 (70 F.), but a softer paraffin is easily made by mixing two parts of 

 the hard paraffin with one part of chrisma or vaseline. The 

 mixture can be made softer by the addition of a little more 

 vaseline, and harder by adding more paraffin. The paraffin 

 mixture is heated on a water-bath or sand-bath until it melts, 

 but its temperature is raised as little as possible above its 

 melting-point. It is convenient to melt it in a porcelain 

 dish with a wooden handle. The tissue is removecT from 

 alcohol, the surplus alcohol removed by wiping it with blotting- 

 paper, until the surface is dry. It is then placed in melted paraffin, 

 and retained in it until the paraffin solidifies. The melted paraffin 

 can be run into embedding boxes of paper (fig. 30), or the embed- 

 ding L's may be used (p. 44), but this simple method is now but 

 rarely used. It has been almost entirely displaced by the following 

 method. 



B. Infiltration Method or Interstitial Embedding. 



1. Embedding in Gum. The tissues after being hardened must 

 have all their alcohol removed by prolonged soaking in water. 

 They are then transferred to gum mucilage, or a mixture of gum and 

 syrup, in which they can be preserved until they are required for 

 freezing, if freezing is to be the process used for cutting the sections. 



Tissues saturated with and embedded in gum mucilage may be 

 hardened in alcohol and then cut. The sections are placed in 

 water, which dissolves out the gum. 



2. Saturation with, or Infiltration with, and Embedding in 

 Paraffin Interstitial Embedding. In this ease the embedding 



