r QF MICROSCOPIC OBJECTS. 99 



where the cells are already filled with other matter, and it is well 

 to mount these with balsam and so gain a greater degree of trans- 

 parency. 



To gain a true knowledge of the structure of bone, sections must 

 be cut as in wood, both transversely and longitudinally ; but with 

 fossil bones, without the lapidary's wheel, &c., it is a laborious 

 task, and indeed can seldom be properly accomplished. In this 

 place, also, it may be mentioned that by submitting bone to the 

 action of muriatic acid diluted ten or fifteen times with water, the 

 lime, &c., is dissolved away and the cartilage is left, which may 

 be cut into sections : in caustic potash the animal matter is got 

 rid of. Both of these preparations may be mounted in fluid. 



The method of cutting thin sections of bone may be also em- 

 ployed with the stones of fruit, vegetable ivory, and such like sub- 

 stances ; many of which show a most interesting arrangement of 

 cells, especially when the sections are transverse. Most of these 

 objects present a different appearance when mounted dry to that 

 which they bear when in balsam, owing to the cells becoming fill- 

 ed ; and to arrive at a true knowledge of them we must have a 

 specimen mounted in both ways. 



To those who study polarized light, few objects are more beau- 

 tiful than the sections of the different kinds of horn. We will 

 briefly inquire into the best method of cutting these. There are 

 three kinds of horn, the first of which is hard, as the stag's, and 

 must be cut in the same manner as bone. The second is some- 

 what softer, as the cow's. The third is another and still softer 

 formation, as the " horn" (as it is termed) of the rhinoceros. In 

 cutting sections of the two last we should succeed best by using 

 the machine invented for these purposes which I shall shortly de- 

 scribe when the method of cutting wood is considered. To aid 

 us in this when the horn is hard it must be boiled for a short time 

 in water, when the cutting will be more easily -accomplished. The 

 sections should be both transverse and longitudinal, those of the 

 former often showing cells with beautiful crosses, the colours with 

 the selenite plate being truly splendid. Of this class the rhino- 

 ceros horn is one of the best ; but the buffalo also affords a very 

 handsome object. The cow's, and indeed almost every different 

 kind of horn, well deserves the trouble of mounting. Whalebone, 



