1. A modification of the standard ester wax 1960 is given which enables sections to be cut at a room temperature of 170 to 37° C (62·6° to 98 6° F).

  2. The melting-point of tropical ester wax is 50° C.

  3. Ribboning and flattening of sections is good, from 1 to 10 p.

Microtomy in a hot room, whether in the tropics or in an overheated building, is generally accomplished by the use of infiltration waxes with high melting-points. This means that during infiltration the specimen is subjected to temperatures about 56° to 60° C. High infiltration temperatures lead to shrinkage and excessive hardness of the specimen, and for these reasons it is an advantage to keep infiltration temperatures as low as possible.

When a solid wax is subjected to increasing temperatures it reaches a point at which it softens and will form a liquid drop. The lowest temperature at which this takes place is the melting-point. When a quantity of the same wax in the liquid condition is gently cooled it reaches a point at which it becomes cloudy, and then it sets or becomes solid. This is the setting-point. With any given wax there is generally a difference of a few degrees between the meltingpoint and the setting-point. The setting-point is lower. It is thus possible, by prolonging the setting period, to keep a wax liquid below its melting-point, though such a condition cannot be maintained indefinitely.

This principle is employed in tropical ester wax 1960, which has the following formula :

Tropical ester wax 1960

diethylene glycol distearate 60 g glyceryl monostearate 30 g

triethylene glycol monostearate 10 g

The mixture will keep liquid at 50° C for about 4 days. After that it begins to flocculate. The liquid wax will become more cloudy if kept at that temperature, but it may be heated to 80°C and filtered. The filtrate will keep clear for another 4 days or more, after which it should be heated and refiltered. It is possible to infiltrate a specimen for any time up to 4 days or even longer, at 50° C.,

Sections and ribbons may be cut at 3 to 10 p when the room temperature is as high as 37·5° C (99° F), after the block has been at that temperature for a week. By keeping the block and knife in cool conditions, such as in a refrigerator at about 15° C, good sections and ribbons may be obtained in a room with a temperature even higher than 37°C.

The sections and ribbons cut in a hot room should always be placed on a soft, rough-surfaced paper, such as duplicating paper. If placed on a smooth, highly calendered paper, the sections will show a much greater tendency to adhere to the paper or to melt.

Tropical ester wax 1960 may be obtained made up and ready for use from the British Drug Houses, Poole, Dorset, England.

Apart from the capacity to withstand higher room temperatures, the wax is similar in all respects to the standard ester wax 1960 (Steedman, 1960).

H. F.
Quart. J. micr. Sci