552 THE MICROSCOPE. 



as little as possible in its subsidence to the sides and 

 bottom of the vessel. This will require two or three 

 weeks, or longer, according to the size and completeness* 

 of the calculi. But I have not found that they increase- 

 at all after six weeks." 



Mr. Eainey shows 1 the analogy or identity of his arti- 

 ficially formed crystals with those found in natural pro- 

 ducts both in animals and vegetables, chiefly confining 

 himself to the structure and formation of shells and bone r 

 pigmental and other cells, and the structure and develop- 

 ment of the crystalline lenses, which he contends are all 

 formed upon precisely the same physical principles as the 

 artificial crystals. Take, for instance, the calculi found in 

 the body : these cannot be distinguished from the crystals 

 of artifically formed carbonate of lime. Again, the shell 

 of the crustaceans ; the resemblance between these and the 

 artificial products is, in some respects, more complete than 

 in that of calculi. All the appearances in shells can, 

 be best observed by merely cleaning them in water, and 

 examining them in glycerine, grinding being unnecessary 

 and injurious. Polarised light is indispensable ; as in the 

 young hermit-crab, at the part where the calcareous and 

 membranous portions of the shell are continuous, the cir- 

 cular forms of globular carbonate are so delicate that no- 

 evidence whatever of its presence can be detected under 

 powerful lenses, and with the best illumination, until 

 polarised light is brought to bear upon the specimen. To 

 obtain the most satisfactory results in the investigation of 

 the process of calcification of animal tissues, it is indis- 

 pensably necessary that the parts examined should be in 

 the earliest stages of the process, and before the calcifying 

 membrane is entirely covered with the globular coalescing 

 deposit. The usual plan of examining shells in thin 

 vertical sections is entirely useless, unless it be simply to 

 see the number and arrangement of their layers ; the part 

 of the section in such specimens, in which the calcifying 

 process ought to be best seen, being entirely ground off. 

 This part, being the softest, can only be preserved in 

 the process of grinding by extreme care, and by keep- 



(1) G. Rainey, "On the Mode of Formation of Shells, Bone, &c. by aprooae oj, 

 Molecular Coalescence." 1858. 



