EXAMPLE 18 



Preparation of a Series of Demonstration Slides, 



Each Having Six Typical Transverse Sections 



of a 72-hour Chick Embryo, Using the Acid 



Alum Hematoxylin Stain of Ehrlich 



Example 3 described in some detail the manner in which a chick 

 embryo can be removed from the yolk and fixed in a Syracuse watch 

 glass, where it is stretched by a collar of filter paper during fixation. Ex- 

 actly the same procedure should be followed in the present instance, save 

 that it is not necessary to leave the hole in the paper of a size larger than 

 will accommodate the embryo itself. The same fixative recommended in 

 Example 3 should be employed, and, after the removal of the fixative, 

 the embryo should be embedded in paraffin by the technique described 

 in Chapter 12. Then the complete series of serial sections should be taken 

 throughout the whole embryo, and the ribbons should be accumulated 

 on a sheet of black paper in front of the worker. 



It is presumed for the purpose of this example that the reader desires to 

 prepare a series of slides for class use on each of which there will be 

 arranged, in order, transverse sections through the regions of the eye, 

 the ear, and the heart, and the anterior, middle, and posterior abdominal 

 regions. In these regions will be found all that is required for the pur- 

 pose of teaching an elementary class the development of the eye, ear, 

 and heart, and the closure of the amnion and neural folds. It is necessary 

 first to identify those sections that will show the required structure and 

 isolate the portions of ribbon containing them. Provided that the sections 

 are placed against a background of black paper, this is relatively simple 

 with the aid of a long-arm, binocular, dissecting microscope, which may 

 be swung over the ribbons and which will supply sufficient magnification 

 to enable the regions of the ribbon to be identified by a competent microt- 

 omist. If the operator has had little practice at this, it might be desirable 

 to stain the embryo in Mayer's carmine before embedding. Then each 

 portion that contains the selected sections is cut from the ribbon with a 



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