The lipoids of the adrenal are difficult to study histologically because of their solubility in the reagents used in paraffin and celloidin embedding techniques. The resulting vacuoles indicate the former resting places of the fat-like substances, but space does not yield much satisfactory information to the inquirer. Protective substances, such as osmic acid, can be used, but they affect only a limited group of chemical radicals, the most common of which is oleic acid.
Frozen sections of fresh or formalin-fixed tissues eliminate the solubility factor, but have other disadvantages. Serial sections are hard to get unless the sections are too thick to be of cytological value. Thin sections fragment easily during the handling iiecessary in staining and mounting, and ice crystals tear the tissues internally.
Gelatin embedding has been used by Nicolas (1895), Olt ('06), and Gaskell ('12) to improve the freezing technique, but these authors had difficulties in the subsequent handling of the tissues.
Our technique consists of: 1. A double embedding in 5 per cent and then 10 per cent gelatin ; refrigeration of the embedded material and cutting into blocks.
The fixed material is washed f o r 4 hours or more to remove all formalin or other fixative and is then put in 5 per cent gelatin in an incubator at 35" to 37Β°C. for 24 hours. It is transferred to 10 per cent gelatin for 12 to 16 hours at the same temperature. The tissue is then embedded in 10 per cent. gelatin ( a Petri dish is convenient) and put in a refrig-