Chap. XVII] URINARY SYSTEM 337 



urine even when no carbohydrates are eaten. This condition is 

 serious because it means that the body tissues are being oxidized 

 to form glucose. The cause of diabetes meUitus is not definitely 

 known. It frequently follows injuries to the head, and is asso- 

 ciated with disease of the pancreas, which interferes with the in- 

 ternal secretion. 



Indican. — Indican is a substance that is formed from indol. 

 Indol results from the putrefaction of protein food in the large 

 intestine. It is absorbed and carried to the liver, which it is 

 thought changes the indol to indican, a less poisonous substance. 

 Traces of indican are found in normal urine, but the presence of it 

 in any amount is abnormal and denotes : (1) excessive putrefaction 

 of protein food in the intestines, or (2) disease of the stomach. 



(1) Excessive putrefaction may be due to a diseased condition of the 

 intestine that interferes with absorption, to a diet containing too 

 much protein food, or to constipation. (2) In certain diseases of 

 the stomach, food is held until it undergoes fermentative changes. 



Acetone. — Acetone is a volatile substance that is thought to 

 be the result of incomplete oxidation of fats and possibly of pro- 

 teins. It is found in the urine of individuals suffering from defec- 

 tive metabolism, and in the urine of normal individuals during 

 periods of fasting. 



Casts. — In some abnormal conditions the kidney tubules be- 

 come lined with substances which harden and form a mould or cast 

 inside the tube. Later these casts are washed out by the urine, 

 and their presence in urine can be detected by the aid of a micro- 

 scope. They are named either from the substances composing 

 them or from their appearance. Thus there are (1) pus casts, 



(2) blood casts, (3) epithelial casts from the walls of the tubes, 

 (4) granular casts from cells which have decomposed and form 

 masses of granules, (5) fatty casts from cells which have become 

 fatty, and (6) hyaline casts which are formed from coaguiable 

 elements of the blood. 



Calculi. — A deposit of solid matter that has been precipitated 

 from the urine is called a urinary calculus or stone. They vary in 

 size, shape, and composition, the size and shape being determined 

 largely by their composition and location. They may be formed 

 in any part of the urinary tract from the tubules to the external 

 orifice of the urethra. The causes which lead to their formation 



