PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS. 215 



The cover having been similarly warmed, a drop of balsam should be 

 placed on it, and made to spread over its surface; and the cover should 

 then be turned over and let down on the object in the manner already 

 described. If this operation be performed over the water-bath, instead 

 of over the spirit-lamp, there will be little risk of the formation of air- 

 bubbles. However large the section may be, care should be taken that 

 the Balsam is well-spread both over its surface and that of its cover; and 

 by attending to the precaution of making it accumulate on one side by 

 sloping the slide, and lltting down the cover so as to drive a wave before 

 it to the opposite side, very large sections may thus be mounted without 

 a single air-bubble. (The author has thus mounted sections of Eozoon 

 three inches square.) In mounting minute Balsam-objects, such as 

 Diatoms, Polycystina, Sponge-spicules, and the beautiful minute spines 

 of Ophiurida, great advantage will be obtained from following the plan 

 suggested by Mr. James Smith, for which his Mounting Instrument 

 (Fig. 130) is specially adapted. The slide being placed upon its slide- 

 plate, and the object having been laid upon the glass in the desired 

 position, the covering glass- is laid upon this, and the ivory knob is ta be 

 screwed down, so as, by a very slight pressure on the cover, to keep in its 

 place. The slide is then to be very gently warmed, and the Balsam to be 

 applied at the edge of the cover, from which it will be drawn in by 

 capillary attraction, penetrating the objects, and leaving no bubbles if 

 too much heat be not applied. In this manner the objects are kept 

 exactly in the places in which they were at first laid; and scarcely a 

 particle of superfluous balsam, if due care has been employed, remains on 

 the slide. When the chitinous textures of Insects are to be thus 

 mounted, they must be first softened by steeping in Oil of Turpentine; 

 and a large drop of Balsam being placed on a warmed slide, the object, 

 taken up in the forceps, is to be plunged in it, and the cover (balsamed 

 as before) let down upon it. It is with objects of this class, that the 

 Spring- Clip (Fig. 128) and the Spring-Press (Fig. 129) prove most 

 useful in holding down the cover until the balsam has hardened suffi- 

 ciently to prevent its being lifted by the elasticity of the object. Various 

 objects (such as the palates of Gasteropods), which have been prepared 

 by dissection in water or weak spirit, may be advantageously mounted in 

 Balsam; for which purpose they must be first dehydrated, and then 

 transferred from rectified Spirit into Turpentine. Carbolic Acid lique- 

 fied by heat has been lately recommended by Dr. Ralph 1 as most efficient 

 in drawing out water from specimens to be mounted in Balsam or 

 Dammar, which afterwards readily take its place. Sections of Horns, 

 Hoofs, etc., which afford most beautiful objects for the Polariscope, are 

 best mounted in natural Balsam, which has a remarkable power of 

 increasing their transparence. It is better to set aside in a warm place 

 the slides which have been thus mounted, before attempting to clean off 

 the superfluous Balsam; in order that the covers may be fixed by the grad- 

 ual hardening of what lies beneath them. 



211. Mounting Objects in Aqueous Liquids. By far the greater 

 number of preparations which are to be preserved in liquid, however, 

 should be mounted in a Cell of some kind, which forms a well of suitable 

 depth, wherein the preservative liquid may be retained. This is absolutely 

 necessary in the case of all objects whose thickness is such as to prevent 



1 See the accout of Dr. Ralph's method in " Journ. of Roy. Microsc. Soc.," Vol. 

 iii. (1880), p. 858. 



