MAKING SECTIONS 67 



it on. Legal-size (foolscap) paper is employed quite commonly and is shown 

 in Fig. 39. Notice that the left-hand edge of the ribbon has been laid flat some 

 distance from the edge of the paper and that a loop large enough to avoid 

 strain on the ribbon attached to the knife is retained with the brush, 

 while the ribbon is cut with a rocking motion of an ordinary scalpel or carti- 

 lage knife. The larger and colder this scalpel is, the less likelihood there is of 

 the section adhering to it. The purpose of leaving a good margin around the 

 edge of the paper is that it may be desirable to interrupt ribbon cutting for a 

 time and to continue later. In this case the worker should furnish himself 

 with a little glass-topped frame, which is laid over the paper to prevent the 

 sections from being blown about. As the inexperienced worker will soon find 

 out, the least draft of air, particularly the explosive draft occasioned by some- 

 one opening the door, is quite sufficient to scatter the ribbons all over the 

 room. These operations of carrying the ribbon out with the left hand, trans- 

 ferring the brush to the right hand, and cutting the ribbon off are continued 

 until the whole of the required portion of the block has been cut and lies 

 on the paper. 



The ribbon must be divided into suitable lengths for mounting on a slide 

 (Fig. 40). Although in theory a section should be of the same size as the 

 block from which it came, this practically never occurs in practice, and it is 

 usually safe to allow at least 10 and sometimes 20 per cent for expansion when 

 the sections are finally flattened. The ribbon should never be cut completely 

 until a sample has been flattened on a slide, in order that one may judge the'' 

 degree of expansion. Though the sections shown in Fig. 41 are mounted on an 

 ordinary 3- by 1-in. slide, it would be more practical for a ribbon as wide as 

 this to use a 3- by lV2-in. or even a 3- by 2-in. slide. The sections should 

 never occupy the whole area of the slide. At least a quarter of an inch should 

 be left at one end for subsequent labeling. When the decision has been made 

 as to how many sections shall be left in each piece of ribbon, the first row of 

 ribbons is cut into the required lengths (Fig. 40). Then the worker must 

 decide what shall be used to cause them to adhere to the slide. It is conven- 

 tional to use: 



Mayer's Albumen: 



Fresh egg white 50 ml. 



Glycerin 50 ml. 



Sodium salicylate 1 Gm. 



The author prefers to dilute the selected adhesive two or three hundredfold 

 with water and to use this diluted adhesive in the next operation of flattening 

 the sections. However, the adhesive can be made full strength and used 



