COLOURING MATTER: MUCUS: EXTRACTIVE. 461 



The nature and composition of the colouring matter of 

 urine are involved in some obscurity. Harley supposes it 

 to be a single substance closely related to the colouring 

 matter of the blood. He terms it Uro-hcematin. 



The mucus in the urine con- 

 sists principally of the epi- 

 thelial debris of the mucous 

 surface of the urinary pas- 

 sages. Particles of epithe- 

 lium, in greater or less abun- 

 dance, maybe detected in most 

 samples of urine, especially if 

 it has remained at rest for some 

 time, and the lower strata 

 are' then examined (fig. 122). 

 As urine cools, the mucus is 

 sometimes seen suspended in it as a delicate opaque cloud, 

 but generally it falls. In inflammatory affections of the 

 urinary passages, especially of the bladder, mucus in large 

 quantities is poured forth, and speedily undergoes decom- 

 position. The presence of the decomposing mucus excites 

 (as already stated) chemical changes in the urea, whereby 

 ammonia, or carbonate of ammonia, is formed, which, com- 

 bining with the excess of acid in the super-phosphates in 

 the urine, produces insoluble neutral or alkaline phosphates 

 of lime and magnesia, and phosphate of ammonia and 

 magnesia. These, mixing with the mucus, constitute the 

 peculiar white, viscid, mortar-like substance which collects 

 upon the mucous surface of the bladder, and is often passed 

 with the urine, forming a thick, tenacious sediment. 



Besides mucus and colouring matter, urine contains a 

 considerable quantity of animal matter, usually described 

 under the obscure name of animal extractive. The investi- 

 gations of Liebig, Heintz, and others, have shown that 



* Fig. 122. Mucus deposited from urine. 



