OF MICROSCOPIC OBJECTS. 97 



substance be too hard for this, the wheel and lathe must be used 

 with diamond dust. If this cannot be procured, there is no alter- 

 native but to rub down the whole substance as thin as practica- 

 ble on some coarse stone or file. The surface will then be rough ; 

 but this may be much reduced by rubbing upon a flat sharpening 

 stone with the finger, or a small piece of gutta-percha, upon the 

 object to keep it in contact. The scratches may be much lessened 

 by this, but not so thoroughly removed as microscopic examina- 

 tion requires in dry sections. It must, therefore, be polished with 

 the putty-powder and dry strop, as recommended in the working 

 of the shell-sections. The other side of the section of the tooth 

 may then be rubbed down to the requisite thinness, and polished 

 in the same manner, when the dust and other impurities must be 

 removed by washing, after which the section must be carefully 

 dried and mounted. Some of these sections are equally interest- 

 ing as opaque or transparent objects. 



The dentine of the teeth may be calcified by submersion of the 

 section in dilute muriatic acid; after drying and mounting in 

 Canada balsam it presents a new and interesting appearance, 

 showing the enamel fibres very beautifully when magnified about 

 three hundred diameters. A friend tells me that after submer- 

 sion of the whole tooth hi the acid he has been able to cut sections 

 with a razor. 



SECTIONS OF BONE. With the aid of the microscope few frag- 

 mentary remains have proved so useful to the geologist and stu- 

 dents of the fossil kingdom as these. From a single specimen 

 many of our naturalists can tell with certainty to what class of 

 animal it has once belonged. To arrive at this point of knowledge 

 much study is necessary, and sections of various kinds should be 

 cut in such a manner as will best exhibit the peculiarities of forma- 

 tion. The methods of accomplishing this will now be considered. 

 It may, however, be first mentioned that the chippings of some 

 bones will be found useful now and then, as 'before stated with 

 flint, though this is by no means a satisfactory way of proceeding. 

 Sometimes the bones may be procured naturally so thin that they 

 may be examined without any cutting ; and only require mount- 

 ing dry or in fluid, as may be found the best. 



When commencing operations we must provide the same ap- 



