RAINEY, ON CARBONATE OF LIME GLOBULES. 31 



how far these ought to be looked upon as crystals^ I shall not 

 attempt to decide ; I may observe, however, that the physical 

 force producing globular shapes is, without doubt, the very 

 opposite of those which produce crystalline ones, and that, 

 even in those cases in which globules are made up of a 

 spherical conglomeration of minute crystals, it may only be 

 where there has been an arrest of that force (attraction) 

 which, though sufficient to bring these crystals into a globular 

 form, would, if its action had extended to their ultimate 

 atoms, also have arranged them in globules. I have now to 

 introduce the account of some very interesting experiments on 

 the reparation of shell-tissue, made by Mr. C. Stewart, of St. 

 Bartholomew's Hospital, confirmatory of observations of the 

 manner in which this class of structures is formed, published 

 by me some years ago. Mr. Stewart's mode of experimenting 

 is entirely his own. The following is a verbatim copy of his 

 letter to me : 



"Dear Sir, — Having repeatedly found that snails, which 

 had suffered from an injury to their shells, had repaired them 

 by the formation of new shelly matter, I thought that they 

 would afibrd a good opportunity for examining the process by 

 which the shell naturally grows. I accordingly removed a 

 portion of the shell of an Helix aspersa, without injuring the 

 animal. I then found, that in a few hours an extremely 

 delicate and perfectly structureless membrane covered the 

 surface of the mantle, and was attached to the edges of the 

 fracture. 



" On examination at the end of two days, the membrane was 

 seen to be covered externally with crystals of phosphate of 

 lime, and also with some compound globules of all sizes, 

 undergoing coalescence into larger ones, as well as very minute 

 particles of lime, of various and more or less regular forms, 

 exactly like those of the carbonate of lime produced artificially. 

 These, no doubt, are formed on the outer side of the membrane, 

 in consequence of its extreme delicacy, allowing the fluid 

 secreted by the mantle, in which the salts of lime are in solu- 

 tion, to percolate through it. 



" On the third or fourth day, the new shell (which is colour- 

 less) is rendered sufficiently strong, by the addition of fresh 

 particles of lime, to allow of the animal being withdrawn from 

 the shell without breaking it. The process of repair now 

 progresses very slowly, it taking months, or even years, to 

 form a perfect and coloured lip, if the injury be to that part. 

 The colouring of the shell I believe to be owing to the pig- 

 ment contained in the cells of the mantle being discharged, in 



