282 TECHNIQUE 



complete ribbon cross-sections of the entire organ, and these have 

 been placed in order in the paper boxes. 



If many sections are to be mounted, the student can use larger 

 slides. After the slide is labelled and the albumen added, then, 

 beginning at the front end of the series of sections, one removes a 

 strip less than 2 inches (1| inches) in length and carefully places 

 this along the edge of the upper surface of the slide, as indicated 

 in the diagram. (Fig. 167). Then adjacent to this, the next strip, 

 and so on. Leave an empty space, about 0.5 cm., along each lateral 

 margin. Place the slide on the warming table, add water, orient, 

 and dry as in single moimts. The number of sections one can 

 get on a slide depends on the size of each section. After completing 

 the mounting of Slide 1, proceed with 2 and remember to label it. 

 Proceed until all the sections are mounted. 



STAINING OF PARAFFIN SECTIONS. 



Thin sections of fresh living material examined with the aid of a 

 microscope appear homogeneous, since there is little optical differ- 

 entiation of cellular structures. Similar examination of fixed tissues 

 which have been cleared reveal more details of structure and 

 organization. These are brought out most distinctly and definitely, 

 however, by the proper treatment of the sections with various dye 

 solutions. The color of the dye or stain is adsorbed, absorbed, or 

 chemically held l)y the different elements of the cell protoplasm in 

 a characteristic manner. Early studies revealed the fact that the 

 nucleus is acid in reaction and has an affinity for basic dyes, while 

 the cytoplasm is basic and has an affinity for acid dyes. When two 

 dyes, one acid and one basic, are used on tissues, the nuclei and the 

 cytoplasm are differently colored, so that a differential staining 

 effect is obtained. Differentiation of various protoplasmic ele- 

 ments has been the aim of munerous staining techniques, so that it 

 is now possible to employ special processes to demonstrate such 

 cellular structures as centrioles, cell mem})ranes, chondriosomes, 

 Golgi apparatus, secretion granules, fat droplets, nucleoli, chromo- 

 somes, chromidia, glycogen, elastic fibers, Xissl bodies, and many 

 others. These s})ecial techniques can be experimented with after 

 the student has become familiar with the more conunon general 

 methods used to demonstrate tissue organizations. 



For this purpose we will describe in some detail a few general 

 techniques. 



Progressive Staining. Tii ])rogressive staining the object is to 

 treat the sections with the stains until the tissue has the ])ro])er 



