46 PHYSIOLOGICAL CHEMISTRY. 



transformation of the organic substances, thus becoming phosphoric 

 acid, which in turn unites with the alkaline bases to form phosphates. 

 In this way some of the superabundant acid is produced, which gives 

 rise to the reaction of the excreted fluids. 



The sodium and potassium phosphates, including the acid biphosphate, 

 are discharged with the urine to the amount of about 4.5 grammes per 

 day. 



8. Sodium and Potassium Carbonates, C0 3 Na 2 and CO :! K 2 . 



The alkaline carbonates, as mentioned above, are associated with the 

 phosphates in all the more important fluids of the body. They are 

 readily soluble in watery fluids, and assist in producing the alkalescence 

 of the blood and secretions. They are partly introduced with the food, 

 where they exist in limited quantity, but they are formed in great 

 measure within the body by the decomposition of other salts of vege- 

 table origin. Certain fruits and vegetables, such as apples, cherries, 

 grapes, potatoes, carrots, and the like, contain inalates, tartrates, and 

 citrates of the alkaline bases. It has been often observed that after the 

 use of fruits and vegetables containing the above salts, the urine be- 

 comes alkaline from the presence of the carbonates. Lehmann found, 

 by experiments upon his own person, that within thirteen minutes 

 after taking 15.5 grammes of sodium lactate, the urine had an alkaline 

 reaction. He also observed that a solution of this substance injected 

 into the jugular vein of a dog, caused the urine to become alkaline at 

 the end of from five to twelve minutes. The conversion of these salts 

 into carbonates takes place, therefore, not in the intestine, but in the 

 blood. The same observer found that, in many persons living on a 

 mixed diet, the urine became alkaline in two or three hours after swal- 

 lowing 0.65 gramme of sodium acetate. 



The organic acid in these cases is decomposed ; and the original salts 

 are thus replaced by the alkaline carbonates, which appear in the urine 

 and modify its reaction as above described. 



A preponderance of vegetable food, accordingly, influences the quan- 

 tity of the alkaline carbonates in the system, and consequently the reac- 

 tion of the excretions. Asa rule, the urine of man and of the carnivo- 

 rous animals is clear and acid, while that of the herbivora is alkaline 

 and turbid with calcareous deposits. Such turbid and alkaline urine 

 will often effervesce with acids, showing the presence of carbonates in 

 considerable quantity. This difference depends upon the alimentation 

 of the animal, and although in carnivorous and herbivorous animals 

 under ordinary conditions the urine is respectively acid and alkaline, 

 if they be. both deprived of food for a few days the urine becomes acid 

 in both, since they are then, in each instance, living upon their own 

 tissues. Furthermore, a rabbit, whose urine is turbid and alkaline 

 while feeding on fresh vegetables, if kept on a diet of animal food, 

 soon produces an excretion which is clear and acid. The reverse effect 

 is produced upon a dog by changing his food from meat to vegetable 



