644 



FUNCTIONS OF ANIMALS. 



has been given of urine, and of the constituents which it con- 

 tains, and the proportion of each voided from an adult in good 

 health during the course of twenty -four hours. The following 

 abstract may be considered as exhibiting an approximation to a 

 mean : 



1. The urea varies from 185-3 grains to 509*3 



2. The uric acid, ... 1'373 ... 14-307 



3. Fixed salts, ... 378- ...748. 



4. Earthy phosphates, 0-447 ... 30-25 



5. Common salt, ... 0-247 ... 116-5 



6. Sulphuric acid, ... 15-25 ... 57-5 



7. Phosphoric acid, 0-17 ... 25-37 



It was long believed by physiologists that urea, uric acid, 

 phosphoric and sulphuric acid were generated in the kidneys by 

 the peculiar action of these organs. This supposition was found- 

 ed on the unsuccessful attempts of chemists to detect these substan- 

 ces in the blood. But MM. Prevost and Dumas showed in 

 1823, that this opinion was ill founded.* They cut out the 

 kidneys of dogs, cats, and rabbits. The animals usually died in 

 about five days after the operation, except the rabbits which did 

 not live so long. On examining the blood of these animals 

 drawn a little before death, they succeeded in finding a consider- 

 able quantity of urea in it. They were not successful in find- 

 ing phosphoric and sulphuric acid in that blood, but their at- 

 tempts were made only in a cursory manner. It is evident from 

 these experiments that the urea in urine is not secreted in the 

 kidneys but only eliminated. Doubtless this is the case with all 

 the other peculiar substances found in the urine. The reason 

 why they cannot be detected in the blood must be, that they are 

 eliminated by the kidneys as fast as formed ; so that they never 

 accumulate in the blood in any sensible quantity. Unless when, 

 by the removal of the kidneys, this removal is prevented. 



The kidneys, then, are not organs of secretion but of elimina- 

 tion. In what organ the urea, uric acid, and other peculiar sub- 

 stances of the urine are formed, is not yet known. It is probable 

 that the albumen, fibrin, or hematosin of the blood, undergoes 

 decomposition in some organ for the formation of some substance 

 useful in the animal economy, and that the urea and uric acid 

 are substances formed at the same time, which not being use- 



* Ann. de Chim et de Phys. xxiii. 90. 



