THE KIDNEYS IX ANIMALS, 787 



fibrinous substance may exude into the uriniferous tubules, and, be- 

 coming coagulated in their interior, form, together with altered epi- 

 thelial cells, or with fatty matter, uric acid, blood or pus corpuscles, 

 little cylindrical masses, known as casts, which are washed out of the 

 tubes, and are easily detected in the urine by the microscope. Some- 

 times the casts consist only of basement membrane. Bright's disease 

 may, however, exist without the presence of albumen in the urine. 



To detect bile in the urine, Pettenkofer's test is used (p. 539). Sugar 

 is detected by Trommer's copper test (p. 546), or by boiling with liquor 

 potassae, which causes a deep brown color when sugar is present. Al- 

 bumen is detected by boiling the urine, and adding a few drops of 

 nitric acid, to make sure that the urine is not alkaline; certain precipi- 

 tates, caused by heat, are then dissolved, but an albuminous precipi- 

 tate remains, as whitish or yellowish flocculi of coagulated albumen. 

 After the continued administration of certain metallic poisons, such as 

 arsenic and antimony, their detection in the kidneys or liver may fur- 

 nish the means of discovering crime. 



As the blood is the most complex fluid proper to the body, being the 

 source of nourishment to the tissues, and also the medium through 

 which the products of their metamorphoses reach the excreting glands, 

 so the urine is by far the most complex of the animal excretions. Its 

 peculiar ingredients display important relations to the gelatinoid and 

 albuminoid principles of the body and of the food, the metamorphoses 

 of which, during the nutrition of the muscular and nervous systems, 

 constitute, with those of the hydrocarbons and carbhydrates consumed 

 in respiration and motion, the characteristic chemical phenomena of 

 animal life. They especially eliminate nitrogen, but also a large 

 amount of carbon, and some hydrogen. The excretion of effete nitro- 

 genous matters by the kidneys may be assisted by the liver ; but 

 most of the nitrogenous fatty acids of the bile are reabsorbed. It is 

 by the kidneys that these nitrogenous products of metamorphosis are 

 constantly being removed ; and if their function be arrested, grave 

 mischief ensues. Ligature of the ureters is followed by an accumula- 

 tion of urea in the blood ; removal of the kidneys, by an increase of 

 the creatin and the creatinin in the blood, and also, though to a less 

 extent, of urea, which is found in the serum ; a urinous odor appears 

 in many of the secretions. In the ursemic poisoning which depends 

 on disease of the kidneys, the urea, ceasing to be excreted through 

 them, is detectible in large quantities in the perspiration, and also in 

 the vomited matters. The urea itself, or the carbonate of ammonia 

 resulting from its decomposition, then easily detected in the breath, 

 circulates through the brain and spinal cord, and causes imperfect 

 respiration, convulsions, coma, and death. 



The Kidneys and the Urine in Animals. 



These important glands, so essential to the animal economy, are well devel- 

 oped in all the Vertebrata, forming, as in Man, two symmetrical organs situ- 

 ated at the back of the abdomen. In Mammalia, as in Man, tke kidneys are 

 composed of an external cortical substance, consisting chiefly of convoluted 

 tubuli, and of an internal medullary substance in which the tubuli are straight. 



