NATURAL SCIENCES OF PHILADELPHIA. 9 



it much surpass the contour of the specimen, otherwise difficulty will be 

 experienced in grinding the second surface. 



In ten or twelve hours remove the binding string, and with a fine saw cut 

 away a portion of the block of matter, or with a file rasp down the adherent 

 piece. But here again method is everything; for a tooth, for example, must 

 be filed from the enamel towards the ivory, otherwise separation will occur. 

 And the same rule is to be observed in grinding down to the second surface. 



lu ouce more resorting to the hones, which, by the way of reminder, ought 

 from time to time to be dressed afresh after the manner already pointed out, 

 it becomes apparent that oil and not witter should be used to moisten and 

 clean the surface. Consequently, the second grinding is. done in oil, and in 

 perfect safety, fur as that fluid exerts no influence upon the glue, the section 

 is retained in position upon the gla-s throughout the process. When, at 

 length, the desired thinness is reached, it will be perceived that the guide 

 papers as well as the section lie equally close upon the surface of the "trued" 

 fine hone, and that they somewhat, resi:?t the action of the stone; and the 

 ground edge of a clean slide applied across the face of the holder will assure 

 the equal thickness of the guide papers and the section itself. If an attempt 

 be made to push the operation farther the holder will be found to adhere some- 

 what tenaciously to the hone. 



The holder must now be carefully wiped clean on all sides; whereupon, 

 after careful examination of the surface for scratches, a polish is to be 

 given. But scratches may be ground oft' with caution, or suftered to 

 remain if they do not compromise essential parts of the specimen. 



With a bit of fine silk stuft' borne upon the finger end, and moistened 

 with oil, take up a little of very fine polishing putty, and rub the adher- 

 ing section quickly as well as briskly, for no heat must be evolved by 

 continued friction, otherwise portions of the specimen will rise in conse- 

 quence of warping, and be broken otf ; or else the polish may be given by 

 means of a small bit of chamois skin fastened upon the end of a phial 

 cork, dampened with oil, and armed with polishing powder. 



Again wipe off the holder with clean soft cambric; then with the same 

 charged with alcohol; next wash the holder rapidly in soap and water, 

 using the finger the while; pour clean water over section and glass, and 

 finally deposit the holder in a glass dish filled with clean water. 



Here let us pause while the water is detaching the section from the 

 paper, and softly liberating the unbroken contour of its margin. The 

 guides are set free, the subjacent paper quits the holder, and the section 

 is left alone by the withdrawal of both paper and glass. 



Before proceeding further I desire to show how sections of very slender 

 rods, spicules, or teeth, such as those of the Bat, may be prepared with faci- 

 lity. As tht^se minute or delicate objects cannot be held by the fingers, the 

 expedient of glueing them to larger objects must be resorted to. But to secure 

 equality in the grinding, the two structures, the supporting and the supported, 

 must be the same. Thus, tooth must be attached to tooth, bone to bone, &c. 

 And as very fragile cancellated tissue will hardly bear the friction of the 

 hones, the meshes are to be filled up with isinglass glue, and the specimen 

 dried before the saw or the hone can be employed. Such specimens must be 

 ground in oil for the first surface ; afier which, when wiped off and robbed of 

 this oil by maceration in chloroform, they may bfe cemented with glue upon 

 the paper-faced holder, and the production of the second surface is accom- 

 plished after the manner already pointed out. 



The support afforded to cancellated tissue by isinglass in the class of objects 

 at present under consideration may be found equally in hardened Canada 

 balsam for objects of another sort. The spines of some Echinoderms are so 

 brittle as not to endure handling in their natural state, but the most ghostly 

 of these, such as the hollow spines of Diadema, may be readily and safely held 

 and [Subjected to the process of grinding if their cancelli be filled with hardened 

 balsam, introduced, of course, while hot. And, to repeat, these small bodies 



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