166 SUMMARY OF CURRENT RESEARCHES RELATING TO 



(3) Cutting-, including- Embedding- and Microtomes. 



New Method of Embedding.* — J. Salkind points out that an 

 aqueous sol of arabin, treated with acetate of lead and exposed to 

 the action of ammonia vapour, is transformed into a gel, which 

 forms an admirable embedding material for the preparation of thin 

 sections. A quantity of cherry-gum (white for preference) is dissolved 

 in double its weight of distilled water. After filtration, add one-third 

 volume of sub-acetate of lead solution (" extrait de Saturne ") with the 

 addition of 5 p.c. acetic acid crystals. The resulting solution, which 

 has the appearance of collodion, is placed in a corked receptacle and the 

 piece of tissue required to be em])edded dropped in. After a sufficient 

 lapse of time (twelve hours for each millimetre thickness of specimen), 

 the cork is removed and the " lead-gum " allowed to evaporate to the 

 consistence of concentrated celloidin. The specimen is placed in a large 

 drop of this solution (or in a paper bos, etc.), and submitted to the 

 vapour of commercial ammonia. The substance hardens rapidly and a 

 block resembling hyaline cartilage is obtained. The block, after being 

 trimmed, is stuck to the platform of the microtome by means of a little 

 " lead-gum " which is then hardened with ammonia gas. When cutting 

 the sections, the block is moistened with 1 in 100 salt solution, in which 

 solution the sections are received. The sections are fixed on the shde 

 bv a modification of Olt's method. The advantages claimed for this 

 method are : the action of fat solvents is avoided (as opposed to the 

 paraffin or celloidin methods) ; there are no variations in temperature 

 (as obtains in the paraffin or gum gelatin methods) ; and there is no 

 hardening action of alcohol or acetone upon certain organs (skin, 

 cartilage, eggs, eyes, and entire insect preparations). 



Preparation of the Knife for Section Cutting.f— Albert Newton 

 says that cutting sections by means of a hand microtome can never be a 

 theoretical success, on account of the number of possible and probal)le 

 errors we always encounter. All these errors can be minimized by care, 

 and as a result hand section cutting is the best method we know of at 

 the present time for some materials. The most likely error is in the 

 knife rocking when passing through the section ; this can be avoided 

 by having the microtome top perfectly level and the knife cutting edge 

 and back both in the same plane. Tlie microtome top is not difficult 

 to keep straight by the following means : — Take a piece of plate-glass 

 and put on it a mixture of water and brass-finisher's sand, keep it in a 

 sloppy condition, and rub the microtome top backwards and forwards 

 until the top has a good bearing surface and is level. On no account 

 use emery powder, as the emery particles embed themselves in the brass 

 table, and will afterwards spoil the knife. To straighten the knife the 

 same plate of glass can be used, but very fine carborundum powder or 

 emery in place of the brass-finisher's sand on account of its quicker cut. 

 If the knife is twisted, grind the back of the blade on an emery wheel 



* C.R. Soc. Biol. Paris, Ixxix. (1916) pp. 811-2. 

 t Trans. Manchester Micr. Soc, 1915, p. 61. 



