`SPREADING FACTOR', USED BEFORE FIXATION, AS AN AID TO CHOLINESTERASE LOCALISATION

There is acknowledged difficulty in securing adequate detail in cholinesterase localisation, especially in sites of low activity. In addition, using the method of Koelle and Friedenwald, modifled by Coupland and Holmes, patchy or incomplete staining was often observed in a variety of tissues. Such preparations were unsuitable for histochemical assessment or for photography. It seemed likely that these shortcomings might be due, in part at least, to uneven fixation or uneven penetration of the fixative. In an attempt to correct or reduce these technical defects, tissues were infiltrated with testis hyaluronidase in isotonic saline, immediately after excision, and afterwards fixed and processed. It was found that hyaluronidase did not bring about diffusion of cholinesterase, as was originally feared. In a controlled series, using a number of tissues, hyaluronidase reduced the number of substandard preparations from 47 % to 6%. Improvement in reliability of the technique was achieved with some tissues, but not with others. Tissues or organs which with the ordinary method showed greatest patchiness seemed to benefit most from the hyaluronidase. It was suggested that speedy fixation with formol-saline can be facilitated with hyaluronidase and, contrasted with freeze-drying, the method has no major drawbacks.