Example 15 x ,;,. 



Preparation of a Series of Demonstration Slides, Each Havmg 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 

 may be removed from the yolk and fixed in a Syracuse watch glass, where it is 

 stretched by a collar of filter paper during fixation. Exactly 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 on page 57. Then the complete series of serial sec- 

 tions 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 purpose of teaching an ele- 

 mentary 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 which 

 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, dissect- 

 ing 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 microtomist. 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 which contains the selected sections is cut from the ribbon 

 with a sharp scalpel which is moved with a rocking motion, picked up on a 

 camel's-hair brush, and transferred to another sheet of black paper. The re- 

 mains of the ribbon may be thrown away. 



The sections in each of the selected strips of ribbon are counted to deter- 

 mine the maximum number of slides which may be made— the ear sections 

 are usually the limiting factor— and the pieces of ribbon trimmed, each to con- 

 tain approximately the same number of sections. Then the required number of 

 slides are cleaned and a few drops of the usual adhesive added to 25 ml. of 

 filtered distilled water in a small flask. 



131 



