75 MOUNTING AND LABELING. 



4. The cover-glass is grasped with fine forceps, the lower side 

 breathed on and then gradually lowered upon the object (PI. II, Fig. 14), 

 and gently pressed down. 



5. After mounting, the preparation is left flat in some cool place till 

 the glycerin jelly sets, then the superfluous amount is scraped and wiped 

 away and the cover-glass sealed with shellac (§§ 168, 169). 



6. The slide is labeled (§ 179). 



7. The preparation is cataloged and safely stored (§§ 1 81-183). 



MOUNTING OBJECTS IN RESINOUS MEDIA. 



§ 175.' While the media miscible with water offer many advantages 

 for mounting animal and vegetable tissues the preparations so made 

 are liable to deteriorate. In many cases, also, they do not produce 

 sufficient transparency to enable one to use sufficiently high powers for 

 the demonstration of minute details. 



By using sufficient care almost any tissue may be mounted in a resin- 

 ous medium and retain all its details of structure. 



For the successful mounting of an object in a resinous medium it 

 must in some way be deprived of all water and all liquids not miscible 

 with the resinous mounting medium. There are two methods of bring- 

 ing this about : 



(A) By drying or desiccation. This answers well for many objects, 

 for example, a fly's wing, crystals, etc. 



(B) By a series of displacements. The first step in the series is 

 Dehydration, that is the water is displaced by some liquid which is mis- 

 cible both with the water and the next liquid to be used. Strong alco- 

 hol (95% or stronger) is usually employed for this. Plenty of it must 

 be used to displace the last trace of water. The tissue may be soaked 

 in a dish of the alcohol, or alcohol from a pipette may be poured upon 

 it. Dehydration usually occurs in the thin objects to be mounted in 

 balsam in 5 to 15 minutes. If a dish of alcohol is used it must not be 

 used too many times, as it loses its strength. 



The second step is clearing. That is some liquid which is miscible 

 with the alcohol and also with the resinous medium is used. This 

 liquid is highly refractive in most cases and consequently this step is 

 called clearing and the liquid a Clearer. The clearer displaces the 

 alcohol, and renders the object more or less translucent. In case the 

 water was not all removed a cloudiness will appear in parts or over the 

 whole of the preparation. In this case the preparation must be re- 

 turned to alcohol to complete the dehydration. 



One can tell when a specimen is properly cleared by holding it over 

 some dark object. If it is cleared it can be seen only with difficulty, as 



