SECRETION. 



457 



URIC SEDIMENTS. These, composed of uric acid and the alka- 

 line and earthy urates, increase the acidity of the urine, render it 

 muddy, and impart to it a brick-red color, which is made more 

 intense by exposure to the air. With the microscope the observer 

 recognizes in the sediment the characteristic crystals of uric acid. 



The precipitation of urates within the bladder is very probably 

 caused by concentration from the absorption of water from the urine. 

 The common belief that holding the urine predisposes to stone is, 

 therefore, justified. Another and more frequent cause of uric sedi- 

 ments in the bladder is the acid fermentation which may occur there 

 from the presence of mucus, as in vesical catarrh. These are strong 

 predisposing causes to uric calculi. 



Fig. 175. Feathery Crystals of Triple Phosphate. 

 (After TYSON.) 



X350. 



OXALIC SEDIMENTS. These accompany the uric sediments, but 

 there may be a predominance of oxalic acid combined with lime. 

 This sediment is recognized by its crystals of calcium oxalate, the 

 "envelope" crystals. They are insoluble in acetic acid. 



They are chiefly observed in deficient respiration, in rickets, in 

 epileptiform convulsions, and in convalescence from serious diseases. 

 The crystals are precipitated by neutralizing the acid urine. This 

 explains why uric calculi are often mixed with oxalic sediments. 

 The acid urine, with its uric sediment, readily becomes neutral and 

 alkaline by reason of purulent catarrh with, therefore, succeeding 

 precipitation of the oxalates. 



