Polyethylene glycols as embedding media in histochemical work.

The embedding and sectioning of tissues in paraffin is a slow process. For histochemical purposes, especially for the demonstration of enzymes, preparation of tissue sections in paraffin is not desirable since the exposures of tissues to high temperatures and to several changes of dehydrating and clearing agents are detrimental to the preservation of enzymes. Gomori's (1946) experience with the technique of histochemical demonstration of acid phosphatase led him to state that " for some reason, the staining for acid phosphatase turns out patchy, occasionally even negative, when it should be positive. This seems to happen, especially in cases when the pieces have been exposed to the temperature of the paraffin oven for more than an hour or when the temperature of the oven is over 560 C." Several investigators (Danielli, 1946; St-afford and Atkinson, 1948; Rabinovitch, Junqueira, and Fajer, 1949) demonstrated severe loss of acid and alkaline phosphatase activity during paraffin embedding of tissues. Montagna and Noback (1947) thought that acid phosphatase was partially denatured during infiltration in paraffin and felt it advisable to eliminate the paraffin method from the technique wherever possible. Rheingold and Wislocki (1948) also find that in the