Müller's Fluid

MÜLLER'S FLUID (N. Müller), or Müller's mixture; consists of 100 cm³ of distilled water, 2.5 g of potassium dichromate and 1 g of sodium sulfate. It is used in pathological-histological techniques for fixation. Fixation lasts about ten weeks or longer, especially for large objects (e.g., an entire brain), which require up to half a year; at 37° fixation is significantly accelerated (to 2-3 weeks). The fluid is taken in large quantities and is changed daily at first, then every 1-2 days or once a week. During this process, it is recommended to continuously increase the concentration of the solution, bringing the content of potassium dichromate up to 5%. Hardened objects are either directly cut on a microtome or thoroughly washed in water (except for the nervous system) and additionally hardened in alcohols of increasing strength. All manipulations are performed in the dark. To prevent putrefaction, small amounts of carbolic acid, camphor, or thymol are added. The disadvantages of Müller's fluid fixation (long duration, possibility of putrefaction of large objects, alteration of nuclear and protoplasmic structure) have necessitated its modification; thus, the Ortmann mixture (10% formalin solution in Müller's fluid) is widely used; one can also first fix the object in 10% formalin and then additionally treat it with Müller's fluid. Müller's mixture serves as a base in a number of histological fixatives; this includes the Zinker (Zenker) mixture, Flemming's mixture, and others. At present, Müller's fluid is used mainly in the processing of the nervous system for subsequent myelin staining, as well as for the purpose of identifying and fixing chromaffin substance.