74 FEEDING ANIMALS. 



one on each side of the spinal column. The right kidney 

 comes forward beneath the two last ribs, whilst the left 

 only reaches the 18th rib. The right kidney is slightly the 

 largest. The urinary secretion is supposed to be simply a 

 filtration of these elements contained in the blood through 

 the tissue of the kidneys. 



The ureters are membranous canals, having about the 

 diameter of a pipe-stem, which convey the urine from the 

 kidneys to the bladder. 



The bladder is a membranous, ovoid reservoir, located in 

 the pelvic cavity, and occupying a space according to the 

 quantity of urine it contains. The bladder serves a most 

 useful purpose in retaining the urine to be voided at con- 

 venient periods. 



The urethra is common to the urinary and generative 



organs. 





 EXCRETIONS. 



The decompositions and oxidations constantly going on 

 in the body charge the blood with carbonic acid, urea and 

 some other nitrogenous products. These must be ex- 

 creted from the body or injury even poisoning would 

 soon result. 



We have seen how the blood is relieved of this excre- 

 mentitious matter by filtering through the tissue of the 

 kidneys and thence passing to the bladder. There has 

 been various theories as to the excretion of nitrogen 

 whether the decomposed albuminoid matter in the body is 

 all excreted with the urine and fasces, or whether some 

 material portion of it is excreted from the lungs and skin. 

 Boussingault, Eegnault and Reiset all held the opinion that 

 nitrogen, in a gaseous form, is excreted from the lungs and 

 skin. This opinion was quite general until the experi- 

 ments of Karl Voit appeared to furnish reasonable proof 

 that urine and the solid dung contained all the nitroge- 



