Notes on the Carbowax Method of Making Tissue Sections

Abstract

In undertaking to employ the water-soluble “Carbo-wax” compounds in making tissues sections, some experimentation was found necessary. These waxes are designated by the average molecular weights of their components except the 1500 grade, which is a mixture of the 1540 variety and the fluid polyethylene glycol 300; no reason is seen for its use in histological work. Different lots of the same designation may vary to some extent in their physical characteristics. The different grades vary greatly in hygroscopicity, the 1000 showing most and the 4000 none, but water taken up is not firmly held. Carbowaxes congeal in crystalline forms which are affected by the way the material is treated; the wax should be melted in the paraffin oven and the blocks cooled in the refrigerator. During infiltration the tissue should be stirred around occasionally, because water is not taken up with avidity. With leprosy skin lesions, infiltrating for 6 hours is preferable to the shorter periods usually specified. Using the 1540 grade (instead of the usual 1500) with the 4000 variety, a 15:85 mixture is satisfactory in our hottest weather, and a 20:80 mixture works well when it is cooler. Blocks which do not ribbon well tend to improve spontaneously, but the trouble may be corrected at once by “doping” the opposite surfaces with 25% beeswax in chloroform. Difficulty in affixing sections is avoided by using dried albuminized slides. Mounting sections on the slide is better done directly than by picking them up from a dish of the flotation material. The effects of a wide range of materials tested as flotants are summarized. The one preferred for ordinary purposes is a very dilute solution of Turgitol 7 with 10% carbowax 1540. Certain aliphatic hydrocarbons are useful for preserving serial relationships, but better is a thin celloidin film on water. Excellent results have been obtained in the staining of leprosy bacilli in carbowax sections.