502 PREPARATION, MOUNTING-, AND COLLECTION OF OBJECTS 



it with a drop of water and rub the slide with the chalked part, 

 then finish with pure water and a clean part of the cloth. 



6. The flattening having been accomplished by either of these pro- 

 cesses, the sections must now be fixed to the slide or cover before the 

 paraffin is removed. 



The most elegant method of accomplishing this is by what is 

 known as the water method. It consists simply in drying the sec- 

 tions on the slide (or cover). After they have been got on the slide 

 and flattened out by water and warming as above described, the 

 superfluous water is drained off, and the slide put away to dry. A s 

 soon as the water has entirely evaporated off, the sections will be 

 found to be so firmly affixed to the glass that they will bear the 

 melting of the paraffin, treatment with solvents, with alcohol or 

 stains, &c., without moving. A convenient plan is to dry the slides 

 on the top of the stove or water-bath at a temperature somewhat 

 under the melting-point of the paraffin. This will take from half an 

 hour to three or four hours. When dry the sections will have 

 assumed a certain horny transparent look. The paraffin must not be 

 allowed to melt before the sections are perfectly dry. If they are left 

 to dry at the temperature of the room, they should be left overnight. 

 As soon as the sections are quite dry, the paraffin may be melted 

 by holding the slide for a few seconds over a small flame, after which 

 it is plunged at once into a tube of xylol or benzol or chloroform or 

 the like, which in a few seconds or minutes dissolves out all the 

 paraffin from the sections. 



The water method is very safe for sections that present a sufficient 

 uninterrupted surface capable of affording adhesion at all points to 

 the slide. But sections of hollow organs, offering only a relatively 

 small surface for attachment, adhere very badly. Sections of such 

 things as tubular chitinous organs, for instance, will generally not 

 allow of mounting at all in this way. 



In such cases, Mayer's albumen fixative should be employed. 

 Take 50 c.c. of white of egg, 50 c.c. of glycerin, and 1 grm. of 

 salicylate of soda, shake them up well together, and filter into a clean 

 bottle. The filtering may take days. A little, very little of this is 

 now painted on to the part of the slide destined to receive the sec- 

 tions, and the layer smoothed by drawing the edge of a slide over it 

 (some persons rub off the excess with the ball of a finger). Place a 

 drop of water on the prepared surface, lay the sections on it and 

 flatten by warming, drain and evaporate as in the water process, 

 with this difference, however, that the evaporation need not be 

 carried to the point of perfect drying. The slides will be sufficiently 

 evaporated at a temperature of 40 C. in ten minutes or a quarter of 

 an hour. And if the evaporation be conducted by waving the slide 

 to and fro over a flame, from three to five minutes may suffice. The 

 paraffin is then melted and removed by xylol or other solvent, as 

 before. This process has the advantage over the water process of 

 greater safety and greater rapidity, but has the disadvantage that 

 the layer of albumen stains obstinately in some plasma stains, thus 

 producing an inelegant mount. 



If the sections be neither rolled nor creased, it is not necessary 



