482 



CHAPTER XXXIV. 



SECRETING GLANDS. THE KIDNEYS. PARENCHYMA. MATRIX. 



URINIFEROUS TUBES. MALPIGHIAN BODIES. CONVOLUTED POR- 

 TION OF THE URINIFEROUS TUBE. STRAIGHT PORTION. VESSELS OF 



THE KIDNEY. OF THE SECRETION OF URINE. URINE. QUANTITY. 



RE-ACTION. CHEMICAL COMPOSITION. UREA. URIC ACID. 



HIPPURIC ACID. CREATINE. CREATININE. EXTRACTIVE MAT- 

 TERS. AMMONIACAL SALTS. FIXED SALTS. CHLORIDES. SUL- 

 PHATES. PHOSPHATES. 



NEXT in size and importance to the liver, are the kidneys. 

 These glands are symmetrical organs, one being placed on each 

 side of the spine in the lumbar region. In consequence of the 

 position of the liver, the right kidney is placed rather lower 

 down than the left. These organs are surrounded by a varying 

 quantity of fat, and are placed behind the peritoneum. The kid- 

 ney is of a dark reddish brown colour, of a firm consistence, and of 

 a close compact texture. Its general form is that of an ordinary 

 French bean, compressed from before backwards, its convex border 

 being external, and its concave edge, or hilum, where the vessels 

 enter, looking towards the median line. The weight of the healthy 

 kidney is from 4 to 5 oz. in the male, and somewhat less in the 

 female. The kidneys are supplied with blood by the renal arteries, 

 two large trunks which come off at right angles from the abdo- 

 minal aorta. The blood is returned by the large renal or emulgent 

 veins which open into the inferior cava. These vessels, with the 

 nerves for the supply of the organ, enter the kidney at its notch or 

 hilum, whence also proceeds the ureter. 



Of the Kidney in the lower Animals. The first trace of an organ which can 

 be regarded in the light of a kidney is met with among the Polypi, but the 

 renal nature of this is at least doubtful. In Porpita, one of the Acalephce, 

 Kolliker has described an organ which contains guanin, and which he there- 

 fore looks upon in the light of a kidney. In the Annelida the existence of a 

 renal apparatus is doubtful ; but there is some reason for believing that the 

 so-called respiratory organs are to be regarded in this light. The existence of 



