S. S. mouse 



PARAFFIN SECTIONS 



139 



purpose since the removal of the salt is 

 more rapid than the acid and bad hy- 

 drolysis may occur at this moment. The 

 mouse should, therefore, be washed with 

 weak (2%) formaldehyde, which should 

 be changed at daily intervals for about a 

 week. At the end of this time the mouse 

 may be washed in running water overnight 

 with safety, and may then be considered 

 ready to be dehydrated and embedded. 

 Before dehydration it is well to trim away 

 as much of the material as can be removed 

 without risk of displacing the remaining 

 internal organs. The larger the piece to be 

 dehydrated and embedded, the longer will 

 the process take, and it is usually per- 

 fectly safe to reduce the preparation at 

 this point to a slab of about yi of an 

 inch thick. Do not hesitate to use fine 

 ligatures of silk to hold in place any organ 

 showing signs of diaplacement, for these 

 ligatures will be missed by the knife as it 

 takes the central section desired. 



Dehydration and clearing can follow 

 the ordinary procedure hanging the slab 

 of tissue at the top of considerable vol- 

 umes of 20%, 50%, 70%, 95%, and ab- 

 solute alcohol before laying it at the bot- 

 tom of a jar containing benzene, which 

 may be changed once or twice. If the 

 mouse has been reduced, as suggested, to 

 a slab, possibly two or three days in each 

 of these alcohols will be sufficient to pro- 

 vide perfect dehydration. As the block is 

 going to be large, plain paraffin would be a 

 most unsuitable embedding medium, the 

 writer warmly recommends one of the 

 rubber-paraffin media, the formula for 

 which is given in Chapter 27 under the 

 heading of E 21.1. In view of the large size 

 of the specimen, the ordinary stender 

 dishes used for embedding will have to be 

 abandoned in favor either of beakers or 

 crystalhzing dishes. It is essential that the 

 specimen should lie flat during the course 

 of embedding, or it will inevitably become 

 distorted, and the care thus far taken to 

 maintain the tail in a straight line with 

 the spine will be wasted. 



The specimen should first be placed in a 

 crystallizing dish filled with benzene, and 

 about a lialf-iiich layer of cliips of the em- 

 bedding medium should be i)laced on to]) 

 of the specimen. The crystallizing dish 

 should be left at room temperature for 



about a day — naturally covered with a 

 plain sheet of glass — and should then be 

 placed in a paraffin oven or warmed to 

 about 50°C. It is necessary to use a 

 special oven for this purpose, because the 

 large quantity of benzol which evaporates 

 from the preparation will be absorbed in 

 any other wax in the oven and render it 

 relativel}^ useless for subsequent embed- 

 ding. Al)out three or four hours later, after 

 the wax has become fluid, this mixture of 

 benzene-paraffin may be enriched by pour- 

 ing molten paraffin into it and carefully 

 stirring it up. One should then at intervals 

 of a few hours — it does not matter leaving 

 it overnight — pour off about half of the 

 fluid contained in the dish and replace it 

 with fresh, molten paraffin. By this means, 

 over a space of a day or two, the specimen 

 may be passed by reasonable gradations 

 from benzene to paraffin. This whole proc- 

 ess should be watched and controlled with 

 the utmost care, for it is easy for these 

 slabs to twist out of shape in the course of 

 impregnation. After the changes described 

 the specimen should finally be removed 

 very carefully to another crystallizing dish 

 containing clean paraffin and left for at 

 least a day to complete the impregnation 

 with wax. 



Casting of the block, which will be too 

 large for a paper box, is one of the few 

 cases in which L-shapecl blocks of brass 

 can profitably be employed. Alternativelj', 

 if L-shaped blocks are not available, take 

 two 1-inch lengths of 1-inch-square brass 

 to form the ends of the box which one is 

 making and attach to them with sealing 

 wax two thin sheets of brass along each 

 side, thus making a metal box. This 

 should be stood on a slab of plate glass. 

 Now pour into this box, which should be 

 at least three inches long by one inch 

 wide and one-and-one-half inches deep, 

 about a half an inch of wax and allow it to 

 cool until it is solid. Then heat, in a small 

 beaker, aliout a teaspoonful of wax to a 

 temperature well above its melting j)oint 

 — it is probabl}' safest to raise it to smok- 

 ing heat — and then pour this suddenly 

 onto the surface of the now hardened wax 

 at the bottom of the box. By this means 

 the surface is again molten and the box 

 can be filled with wax which has been 

 maintained in the oven at about its melt- 



