EXCRETION 439 



acid ammonium urate in the form of dark balls occasionally covered 

 with spines (Fig. 165). Calcium phosphate (CaHPO 4 ) is another 

 phosphate found in sediments deposited from alkaline or faintly acid 

 urine. It is usually amorphous, but sometimes in the form of long 

 prismatic crystals arranged in star fashion, and hence spoken of 

 as stellar phosphate (Fig. 164). It is not pigmented. 



It is only in pathological conditions that the alkaline fermentation 

 takes place within the bladder. The reaction^ of the urine can 

 readily be made alkaline by the administration of alkalies, alkaline 

 carbonates, or the salts of vegetable acids like malic, citric, and 

 tartaric acid, which are broken up in the body and form alkaline 

 carbonates with the alkalies of the blood and lymph. It is not so 



o 



FIG. 162. TRIPLE PHOSPHATE. FIG. 163. CYSTIN. 



easy to increase the acidity of the urine, although mineral acids do 

 so up to a certain limit. If the administration of acid be pushed 

 farther, ammonia is split off from the proteins, and is excreted in the 

 urine as the ammonium salt of the acid. 



Determination of the Acidity. A titration method is described in 

 the Practical Exercises (p. 477). In speaking of the reaction of 

 blood, it has already been mentioned (p. 24) that we cannot deter- 

 mine by titration the true acidity or alkalinity of a liquid in the 

 physico-chemical sense i.e., the concentration of the dissociated 

 hydrogen and hydroxyl ions respectively. E.g., when we titrate 

 equal quantities of decinormal* acetic acid and decinormal hydro- 

 chloric acid with decinormal potassium hydroxide, using, say, phenol- 



FIG. 164. STELLAR PHOSPHATE FIG. 165. AMMONIUM URATE 



CRYSTALS. (AFTER MILROY). 



phthalein as the indicator, nearly the same volume of the potassium 

 hydroxide solution will be needed to neutralize each acid. Yet 

 it can be shown by physico-chemical methods that the acetic acid 

 in the strength used is only dissociated to the extent of a little more 

 than i per cent., while about 80 per cent, of the hydrochloric acid 

 is dissociated. The concentration of the hydrogen ions is there- 



* A normal solution of a substance contains in a litre a number of 

 grammes of the substance equal to the number which expresses its 

 equivalent weight a decinormal (usually written ^) solution one-tenth 

 of this amount, a centinormal one-hundredth, etc. Thus, a normal 

 solution of potassium hydroxide contains 56 grammes of KOH, and a deci- 

 normal solution 5 '6 grammes in 1000 c.c. 



