DS 11.10 



DYE STAINS OF GENERAL APPLICATION 



279 



may be removed from the yolk and fixed 

 in a Syracuse watch glass where it is 

 stretcliod by a collar of filter paper. Ex- 

 actly the same procedure should be fol- 

 lowed in the present instance, save that 

 it is not necessary to make the hole in the 

 paper a size larger than will accommodate 

 the embryo itself. The same fixative rec- 

 ommended there should be employed, but 

 after the removal of the fixative, the 

 embryo should be embedded in paraffin 

 and cut by the methods described in 

 Chapter 12. A complete ribbon of serial 

 sections should be taken from the whole 

 embryo. 



It is presumed for the purpose of this 

 example that the reader wishes to have a 

 series of slides for class use, on each of 

 which will be arranged, in order, trans- 

 verse sections through the region of the 

 eye, the ear, the heart, and the anterior, 

 middle and posterior abdominal regions. 

 These regions will be found all that is re- 

 quired for teaching an elementary class 

 the development of the eye, ear, and heart, 

 and the closure of the amnion and neural 

 folds. It is first necessary to identify those 

 sections which will show the required 

 structure and to isolate the portions of 

 ribbon containing them. Provided the sec- 

 tions are placed against a background of 

 black paper, this is relatively simple with 

 the aid of a long-arm binocular dissecting 

 microscope. This microscope may be 

 swung over the ribbons and will supply 

 sufficient magnification to enable the re- 

 gions of the ribbon to be identified by a 

 competent microtomist. If the operator 

 has had little practice at this, it might be 

 desirable to stain the embryo in carmine 

 before embedding, preferably with one of 

 the alum-carmines given in section DS 

 11.21 below. Each portion which contains 

 the selected sections is then cut from the 

 ribbon with a sharp scalpel moved with a 

 rocking motion, picked up on a camel's- 

 hair brush, and transferred to another 

 sheet of black paper. The rest of the 

 ribbon may now be thrown away. 



The sections in each of the selected 

 strips of ribbon are then counted to 

 determine the maximum number of slides 

 which may be made — the ear sections are 

 usually the limiting factor — and the 



pieces of ribbon are trimmed so that 

 each contains approximately the same 

 number of sections. The required num- 

 ber of slides are then cleaned and a few 

 drops of the usual adhesive added to an 

 ounce or so of filtered distilled water in a 

 small flask. 



The only difficulty of this procedure is in 

 fixing each section in its correct place on 

 the shde. A single shde is taken, placed in 

 front of the operator, and covered lightly 

 with the dilute adhesive. The fluid should 

 extend to the edge of the sUde, but should 

 not be raised in a meniscus sufficiently 

 high to cause any appreciable slope of the 

 fluid from the center of the sUde toward 

 the edges. The end section is then cut 

 from each of the ribbons with a sharp 

 scalpel with a rocking motion. These sec- 

 tions are then placed in the correct order 

 (but without any regard to symmetry) on 

 the surface of the fluid on the shde. To 

 secure these sections in the required posi- 

 tion it is now necessary to have two fine 

 brushes, a mounted needle, and a bunsen 

 or spirit lamp. 



The last section, that is, that section 

 which is required to he farthest from the 

 label on the sUde, is now secured in posi- 

 tion with a brush held in the left hand, 

 wliile the second section is maneuvered 

 with a brush held in the right hand until 

 its edges touch those of the first section. 

 Both sections will be held together by 

 capillary attraction when the brush is 

 removed. The needle is then warmed in 

 the flame and used to fuse the edges of the 

 sections together in two spots. If the en- 

 tire edge is melted it will create a ridge 

 which will prevent the compound ribbon 

 from lying flat against the shde. Two 

 minute spots fused together with the point 

 of the needle are quite sufficient to hold 

 the section in place. The brush is again 

 picked up with the right hand and used to 

 guide the next section into its appropriate 

 place. This section is then spotted into 

 position with the tip of the w^arm needle, 

 and so on, until all the sections have been 

 fused into a continuous ribbon. The rib- 

 bons are then flattened w-ith heat and 

 drained as described in Chapter 12. The 

 sections are now, in the ordinary course of 

 events, left on the warm table until they 



