LIVER. 83 



for secretion (the epithelial cells of the urinary tubules), it might be inferred 

 that the elimination of the constituents of the urine is accomplished by the 

 twofold process of filtration and secretion; that the water and highly 

 diffusible inorganic salts simply pass by diffusion through the walls of the 

 blood vessels of the glomerulus into the capsule of Miiller, while the urea 

 and remaining organic constituents are removed by true secretory action of 

 the renal epithelium. Modern experimentation supports this view of renal 

 action. 



The secretion of urine is therefore partly physical and partly vital. 



The Filtration of urinary constituents from the glomerulus into Miiller's 

 capsule depends largely upon the blood pressure and the rapidity of blood 

 flow in the renal artery and glomerulus. Among the influences which 

 increase the pressure and velocity, may be mentioned increased frequency 

 and force of the heart's action, contraction of the capillary vessels of the 

 body generally, dilatation of the renal artery, increase in the volume of the 

 blood. 



The reverse conditions lower the blood pressure and diminish the secre- 

 tion of urine. 



The elimination of the organic matters by secretory activity of the renal 

 epithelium seems to be well established by modern experiments. These 

 substances, removed from the blood in the secondary capillary plexus of 

 blood vessels, by a true selective action of the epithelium, are dissolved and 

 washed toward the pelvis by the liquid coming from the capsules. 



The blood supply to the kidney is regulated by the nervous system. If 

 the renal nerves be divided, the renal artery dilates and a copious flow of 

 urine takes place. If the peripheral ends of the same nerves be stimulated, 

 the artery contracts and the urinary flow ceases. The same is true of the 

 splanchnic nerves, through which the vasomotor nerves coming from the 

 medulla oblongata and spinal cord pass to the renal plexus. 



LIVER. 



The Liver is a highly vascular, conglomerate gland, appended to the 

 alimentary canal. It is the largest gland in the body, weighing about 4^ 

 pounds ; it is situated in the right hypochondriac region, and retained in 

 position by five ligaments, four of which are formed by duplicatures of the 

 peritoneal investment. 



The proper coat of the liver is a thin but firm fibrous membrane, closely 

 adherent to the surface of the organ, which it penetrates at the transverse 



