15 



In the herbivora the reaction is normally alkaline and is 

 due to the presence of bicarbonates or carbonates of lime or 

 potassium. It would appear that the salts present in the 

 vegetable food undergo oxidation to form organic acids, and 

 these in turn are transformed into bicarbonates or carbonates, 

 causing alkalinity of the urine. 



In man the acidity is due to the presence of acid sodium 

 phosphate NaH^ PO^. The urine passed before breakfast and 

 during fasting or perspiration is more acid than at other times ; 

 during digestion and after meals the acidity is decreased. 



The degree of acidity of the urine may be determined by 

 the use of the acidimeter. a graduated glass tube devised by Dr. 

 H. R. narrower. His description of it and its use follows: 



The acidimeter consists of a glass tube so graduated that 

 10 cc. is the first measuring point. From this upward the tube 

 is graduated in fifths of degrees up to 100°, each degree repre- 

 senting the amount of decinormal sodium hydroxide solution 

 required to neutralize 100 ee. of urine. The method of using 

 the acidimeter is as follows: The tube is filled with the urine to 

 be tested, until the lower edge of the meniscus is just on the 

 10 cc. mark. Two drops of phenolphthalein indicator solution 

 are added, and then with an ordinary medicine dropper deci- 

 normal sodium hydroxide solution is slowly added, inverting 

 the tube after each addition, until the color of the fluid has just 

 been changed from a yelloAv to a light rose pink. The acidity in 

 degrees is now read off on the tube at the level of the fluid. The 

 normal acidity of a mixed 21: hour specimen should be between 

 30 and 40 degrees. 



(With very concentrated urines in which the acidity is 

 above 100° the tube may be filled to the 5 cc. mark and water to 

 the usual level. The resulting figures are, of course, doubled.) 



If the urine is alkaline in reaction and it is desired to esti- 

 mate the degree of alkalinity decinormal hydrochloric or oxalic 

 acid solution must be used in place of the sodium hydroxide, 

 the pink color present being just discharged by the acid." 



The "Acid Index" or "Acid Unit" may be obtained by 

 multiplying the degree of acidity by the amount of urine passed 

 in 24 hours. The normal in man is about 40,000 acid units. 



In man there is increased acidity physiologically during the 



