This section is from the book "A Manual Of Pathology", by Guthrie McConnell. Also available from Amazon: A Manual Of Pathology.
The preparation must be thoroughly dehydrated in absolute alcohol or anilin oil. It is then placed in some fluid that is a solvent of paraffin - xylol or chloroform are commonly used - for four to five hours. The fluid should be changed several times. Then it is put in a mixture of chloroform or xylol and paraffin for two to three hours. The infiltration is hastened by heating the mixture at about 500 C. It is then placed in paraffin that melts at about 500 C. for three to five hours, the paraffin having been changed once or twice. The melting-point can be varied by making combinations of paraffin that melt at different degrees. The two generally used are one of 56° C. and another of 45° C. In warmer weather a paraffin with a higher melting-point is used.
The specimen is taken and placed in a little paper box in which a small amount of paraffin has been poured. When the tissue has been properly arranged, more paraffin is added. The box is then placed in a dish of cold water, so that it will be rapidly cooled. This prevents crystallization and brittleness. Instead of using the paper boxes two right angles of metal are put on a glass plate so as to form an enclosure. Paraffin is poured in to form a thin film, then the tissue, and finally more paraffin.
After cooling, the specimen is fastened on a block of vulcanite or hard paraffin by heating its surface, and is then cut on the microtome. The blade is held at a right angle if the specimen is small, on a slant if large, and the cutting is done dry, no alcohol being used.
Summary of the paraffin embedding:
1. Dehydration in -absolute alcohol.
2. Xylol or chloroform four to five hours, changing the fluid a couple of times.
3. Xylol or chloroform and paraffin, two or three hours.
4. Melted paraffin in hot chamber at 500 C. for three to five hours. Change once.
5. Block and quickly cool.
The paraffin sections are so brittle that they cannot be treated in the same way as the celloidin ones. The best method is to take the section and place it in a dish containing water at about 450 C. This causes the specimen to flatten. A perfectly clean slide is then smeared with a very fine film of glycerin-albumin and is slipped under the floating section. The excess of water is drained off or carefully touched with blotting-paper and the slide is then placed in the incubator at 370 C. for three to five hours.
The paraffin should be removed before staining the section. This is hastened by holding the slide over a small flame until the paraffin becomes transparent, when it is placed in xylol or turpentine for about two minutes. From there into absolute alcohol for about five minutes. It is advisable but not necessary to put the slides into weaker alcohol before beginning the stain. When the above steps have been gone through the tissues may be stained any way that is desired.
Glycerin-albumin solution for fastening paraffin sections to the slide is made as follows: The white of an egg is well beaten and to it is added an equal volume of glycerin. These are thoroughly mixed and filtered. It is used by smearing a very thin layer on the slide, the paraffin section is placed on it and then heated up to a temperature of about 6o° C. until the albumin coagulates. If the sections have been taken from water it must be allowed to evaporate before the coagulating is done. The evaporation will be hastened by placing the slides in the incubator.