KATURAL SCIENCES OF PHILADELPHIA. 7 



wards attached by moderately hard balsam to the slide on which it is to 

 remain, and the final surface will be reached by a repetition of the pro- 

 cess of grinding. And here I would call attention to some points in the 

 manipulation, which are that in reducing any substance to the condition of a 

 lamina, it should be poised securely with the fingers, whether it be free or 

 cemented upon glass; propelled along the face of the hone with a long, even 

 and steady sweep ; and turned repeatedly' upon its horizontal axis. A polish 

 may be given or not, according to the nature of the substance, and the sec- 

 tion may be regarded as finished if it bear a satisfactory examination under 

 the microscope. And it should not be forgotten that many specimens are 

 best prepared by working them up to the power under which they are des- 

 tined to be studied. 



Hardened organic substances, as the crystalline, do not bear the heat ne- 

 cessary for attachment to a glass slide, wherefore the second surface must 

 be produced by fixing the first surface upon a bit of white wax by gentle pres- 

 sure. 



Finally, after the grinding shall have been completed, it will be necessary 

 to clean the slide with water ; and after drying, to wash away the powder 

 and debris adherent to the surrounding film of balsam with chloroform passed 

 lightly over the slide by the finger covered with soft linen, or, if the section 

 will endure such treatment, the whole of the margined balsam may be 

 cleared away by pouring over the slide a stream of chloroform. But turpen- 

 tine should be used to detach a finished section from wax. 



To mount such sections it will be found advantageous to moisten them with 

 turpentine before dropping on the thin balsam. The cover glass is to be 

 applied warm, and a small weight, as an inch or even a half inch screw placed 

 on it as eventually to press out superfluous balsam. I say eventually, because 

 such slides are unfit for use for several weeks. 



When the balsam shall have become sufficiently tenacious the slide may be 

 cleaned by passing a knife blade, held fiat, from the cover glass into the cir- 

 cunivalhile cement, and then boldly away over the slide. What remains is 

 to be removed with a solution of caustic potash, which itself calls for a free 

 watery ablution, and then the slide needs nothing but the label. 



This method o"f mounting sections is applicable to a great variety of ob- 

 jects, and will be found to yield the best results in the case of urinary crys- 

 tals, of the so-called heraatin crystals, or of the chitinous skeletons of insects 

 as actually practised by the incomparable Mr. T. W. Starr, of Philadelphia. 



The preparation of objects of the second class is attended with difficulties, 

 some of which are to be overcome by means similar to those emploj'cd in 

 manipulating objects belonging to the former, and some, by reason of the na- 

 ture of the objects themselves, are to be surmounted by a resort to various 

 expedients. Thus, sections of spines of Echinodermata, as also of biliary 

 and other calculi, may be made in the same way as sections of harder sub- 

 stances ; that is, by grinding down a true surface by means of fine silex and 

 finer pumice with water, fixing that side, when dry, upon a slide with Canada 

 balsam hardened until it has become very " tacky," and then finishing the 

 second surface in the same manner as the first. But the calculi, generally, 

 must not be removed from the slide, although the marginal balsam may be 

 cleaned away by drops of chloroform ; and they must be covered with soft 

 balsam in situ and so covered. The spines, however, may and must be en- 

 tirely cleaned by repeated drops of chloroform, in which they are to be floated 

 away from their early attachment ; whereupon the slide being wiped clean in 

 the middle, the section is to be floated back to tlie central spot, suffered to 

 dry, then moistened with turpentine, and immediately overflowed with soft 

 balsam. Heat may or may not be employed before applying the cover glass. 



The trick of sectionizing a very small spine of Echinus, or similar object, 

 consists in perforating a disc of a large spine, saturating it with hardened 

 balsam, and inserting the capillary spine into the perforation, aided by heat. 

 The two substances ought to be the same. Now grind down the large piece ; 

 and when finished and washed out, find, separate and mount the particle. 



