For imbedding large pieces of tissue in celloidin a glass dish may be filled with thick celloidin and the infiltrated tissue placed in it with cutting surface down. The celloidin is then allowed to evaporate slowly under a glass cover, and fresh celloidin may be added as shrinkage occurs. When well-hardened the celloidin is cut out of the dish and the block trimmed to the proper proportions, and attached directly to the object-holder of the microtome or to a block of wood by a few drops of thick celloidin, allowing it to dry for a minute or so and then immersing in 80 per cent alcohol. The block may be cut on the freezing microtome by soaking the hardened celloidin in water to remove the alcohol (when block sinks), then coating it with saturated gum arabic solution, and freezing. Rapid Celloidin Method. I have used the following method in my laboratory for a number of years as a regular procedure in practical diagnostic work, and the results have been uniformly good. 1. Fresh tissue cut thin, or uterine curettings, in absolute alcohol 1½ hours, three changes of fresh absolute during this time. 2. Alcohol-ether 1 hour. 3. Thin celloidin at incubator temperature 12 hours (over night). 4. Medium celloidin 1 hour. 5. Block from medium celloidin, evaporating celloidin by blowing, and building up matrix by adding successive layers of celloidin. 6. 80 per cent alcohol 1-3 hours. 7. Cut. The quick celloidin methods recommended in the literature (Kaufmann, Stepanow, Scholz and others) require more time, and do not give better results. Material received from operative clinics late in the afternoon can be sectioned and stained usually by ten o’clock the next morning. 2. =PARAFFIN IMBEDDING.= A paraffin of a melting-point sufficiently high enough to withstand summer heat is advisable; a 52°C. paraffin answers for this latitude. The use of softer paraffins is not necessary. The paraffin-oven should be regulated at a constant temperature of 54-55°C. Over-heating of the tissue while in the oven must be carefully safeguarded, so that in the management of a paraffin-oven the care of the thermo-regulator is the most important thing. Slow Paraffin Method. 1. Thorough dehydration in absolute alcohol 12-24 hours. 2. Aniline oil to remove alcohol, until tissue becomes transparent or sinks. 3. 1st. Xylol, ½ hour, to remove aniline oil. 4. 2nd. Xylol, 1-2 hours, until translucent. 5. 1st. Paraffin, 52°C. in oven, 1 hour, to remove xylol. 6. 2nd. Paraffin, 52°C. in oven, 1-12 hours. 7. Block.