AND OTHER URINARY DEPOSITS 95 



bodies. The stalactites which depend from the roofs 

 of our limestone caverns show an analogous structure. 



The most marvellous natural illustration of con- 

 cretionary action is the so-called Gotham or landscape 

 marble, which occupies only a single geological 

 horizon, but is widely distributed throughout the 

 south-west of England. All the foliated layering of 

 an oxalate calculus is reproduced in the marble, 

 but with the addition of tall " trees " with " branches " 

 rising to a " sky " composed of thickly stratified 

 microcrystalline layers. 



It was shown long ago by Rainey that the desidera- 

 tum for calculus formation is the presence of some 

 glutinous matter in the solvent. He was able to 

 manufacture small concretions of calcium carbonate 

 by allowing an alkali and a lime salt very gradually 

 to interdiffuse in the presence of gum. A nucleus 

 also is very desirable. 



If the simple experiment be made of allowing urine 

 to undergo ammoniacal fermentation in a closed flask 

 over a layer of gelatin, the raison d'etre of this is 

 clearly seen. The urine should be replaced every 

 other day by fresh, leaving the deposit of triple 

 phosphates undisturbed. When the experiment is 

 carried out without a gelatin layer, the crystals 

 deposited are all separate. When, however, there is a 

 gelatin layer at the bottom of the flask, extensive 

 films form on the surface and the sides, composed 

 of hundreds of minute crystals stuck together. 

 Evidently a succession of such films, deposited con- 

 centrically around a nucleus in the bladder, would 

 make up a concretion or calculus. 



