WITH THE MICROSCOPE. 69 



PART II. 



UF PREPARING AND PRESERVING OBJECTS FOR THE MICROSCOPE 

 SEPARATING DEPOSITS FROM FLUIDS OF INJECTING OF DE- 

 MONSTRATING THE STRUCTURE OF THE FULLY FORMED TISSUES 

 OF MAN, THE HIGHER AND LOWER ANIMALS, AND PLANTS OF 

 EXAMINING MINERALS AND FOSSILS. 



OF THE IMPORTANCE OF EXAMINING THE SAME OBJECTS IN 

 DIFFERENT MEDIA AIR, WATER, AND CANADA BALSAM. 



Many objects require to be studied in different ways before an 

 accurate idea of their general structure can be formed. It is in many 

 instances of the utmost importance to examine an object by reflected 

 light as well as by transmitted light, and to observe the peculiarities 

 of structure when it is surrounded with air, or immersed in water, or 

 in a highly refracting fluid, such as glycerine, oil, turpentine, or Canada 

 balsam. Not less valuable is the information we derive from the 

 application of certain chemical reagents (part III). The method of 

 investigation must vary according to the degree of transparency or 

 opacity, density, refractive power, and chemical composition of the 

 specimen. The object must also be examined first with the aid of 

 low, and afterwards with high magnifying powers. 



136. Appearance or the same Object examined in Air, Water, and 

 Canada Balsam, by Transmitted Light, and under the Influence of 

 Reflected Light and Polarised Light. In pi. XIX specimens of the 

 same structure (spherical crystals of carbonate of lime and octahedra 



of oxalate of lime) magnified in the same degree, are represented. 

 In Air. In fig. 113 crystals of carbonate of lime, and in fig. 119 



octahedra of oxalate of lime are shown by transmitted light in air 

 mounted in the dry way, and it will be noticed how very dark and 

 thick the outer part appears, and how impossible it is to make out 

 the structure of the former crystals. 



/// Water. In figs. 114 and 120 the same crystals are seen in 

 water. The outer part of the crystals of carbonate of lime is still 

 very dark and thick, but a few lines may be observed radiating from 

 the centre of the crystals towards their circumference, although not 

 very distinctly. 



