RAINEY, ON CARBONATE OF LIME GLOBULES. 29 



of carbonate of lime, I may state that I am perfectly aware 

 that there are other cases in which carbonate of lime may be 

 made to take the globnlar form. In this respect it seems to 

 be a compound like salicine, asparagine, and some others, in 

 which the force causing the crystalline form is feeble, and there- 

 fore easily overcome by that which causes particles to become 

 globular ; but this does not in the least affect the fact of car- 

 bonate of lime, when formed ir> a sufficiently strong solution of 

 gum or albumen, becoming globular, or its applicability to the 

 organism in which this compound .is produced, as experi- 

 ment shows that it is in such a state of combination as this 

 that it occurs in organic tissues. To show the effect which 

 gum has in determining the form of carbonate of lime, slides 

 were put into bottles containing the same alkaline solution, 

 which in all was as much inspissated as possible to be fluid, 

 but the simple solution of gum was of different densities in 

 each bottle. The slides were removed from the solutions in 

 about four weeks. The carbonate on those which had been 

 in the densest solution was all either in globules or dumb- 

 bells. There were no crystals, whilst that deposited on the 

 slides taken out of the weakest solution was in globules 

 below, that is, near to the surface of the dense alkaline solu- 

 tions, but in crystals above, where the quantity of gum in the 

 solution was smallest. All these crystals examined from 

 above downwards were seen gradually to lose their crystalline 

 form, having their angles gradually rounded and their sides 

 variously curved ; after that they assumed the character of 

 dumb-bells of different forms, and lastly they became globules. 

 Fig. 7 is an accurate representation of the forms of carbonate 

 of lime on one of these slides. The other slides presented 

 various forms of carbonate intermediate between those 

 extremes, but fully confirming the correctness of the conclu- 

 sion that the globular form is due to the gum, and that the 

 various modifications of the crystalline forms, as shown in 

 the figure just referred to, are dependent upon the relative 

 quantities of gum and carbonate of lime entering into their 

 composition. Now, it is worthy of remark that all these 

 various forms exist in calcified tissues. In some, the crystal- 

 line form prevails, especially in the densest shells, and in 

 those parts of the less dense ones which are the hardest. In 

 others, the globular form most abounds, a,nd especially where 

 the shell is in an incipient stage of growth, and before the 

 membrane on which the carbonate is formed is entirely 

 covered by coalesced particles ; and lastly, there are shells, as 

 that of the shrimp and prawn, which present both globules 

 and modified crystals near together. 



