370 



HEALTH AND DISEASE 



inner portion of the stone is the more hard and compact, while the outer 

 portion is less consistent, and, in some instances, so soft as to be readily 

 broken down with the fingers into small rounded or angular fragments. 

 To examine the structure of these formations the stone should be first cut 

 with a saw and the divided surface rubbed even and smooth on a wet stone. 



If the polished face be now examined it will 

 be seen to present certain structural mark- 

 ings, of which the following are the more 

 common examples: 



1. A regular series of closely -arranged 

 concentric rings (fig. 163), representing sec- 

 tions of a succession of layers of earthy 

 matter.' Of these some are narrow, some 

 broad, some yellow or pale brown, and we 

 gather, by the use of the knife, that they are 

 soft or hard according as they have been 

 quickly or slowly deposited. In this variety the stone, as a whole, is 

 usually hard and its texture compact. 



2. The laminae are irregular and incomplete, sometimes interrupted 

 by small sinuous cavities or irregular spaces containing free earthy granules 

 and epithelial debris. 



3. Sectional surface irregular, and marked by sinuous fissures (fig. 

 164). Centre excavated and enclosed by a narrow strong band, from 



Fig. 163. Section of Vesical Calculus 



Fig. 164. Section of Vesical Calculus 



Fig. 165. Section of Vesical Calculus 



which arborescent rays proceed to the circumference and terminate in 

 asperities on the surface, giving to the section a rough, coarse appearance. 



4. Small groups of concentric rings forming rounded, solid - looking 

 bodies varying from the size of a hemp-seed to that of a bean (fig. 165). 

 They are separated from each other by a structureless mass of earthy 

 matter, usually of less density than themselves, and in which fissures 

 and cavities are sometimes met with. This variety consists of a number 



