452 PHYSIOLOGY. 



In serious diabetes there is an abundant production of organic 

 acids not convertible into carbonic acid in the body. Such are the 

 acetylacetic and beta-oxybutyric, which must be neutralized by 

 bases, such as ammonia, which is derived from the meat used as food 

 and from the proteid metabolism of the cells of the body. When 

 this ammonia does not suffice to neutralize the acid, then the sodium 

 of the blood is called upon; the blood becomes less alkaline. But 

 the sodium of the blood is necessary to form a combination with the 

 carbon dioxide for it to make its exit from the lungs. 



Coloring Matters of the Urine. The two main coloring matters 

 of the urine are urochrome and urobilin. Under normal physiological 

 conditions, urine may range from an almost colorless or pale straw- 

 yellow through intermediate shades until reddish brown is reached. 

 The commonest condition is yellow. Pale urine is usually of low 

 density; high-colored, of high density, dependent upon the con- 

 stituents excreted by the renal epithelium. In addition to the two 

 main coloring matters may be mentioned uroerythrin and hcemato- 

 porpliyrin; these four are not the only chromogenic factors in the 

 urine, but are the ones that are best known to us to-day. 



UROBILIX, like bile-pigment, is an iron-free derivative of hemo- 

 globin. In normal urine it occurs in very small amounts and almost 

 always as a cliromogen; only rarely is it found free in physiological 

 urine. In diseases it is commonly increased, especially in the highly 

 colored urines of feverish patients. It gives to the urine a peculiar 

 reddish color. 



Urobilin is identical with stercobilin. The theory usually ac- 

 cepted concerning its mode of origin is that bile-pigment is con- 

 verted in the intestines into stercobilin; while the major portion of 

 the stercobilin leaves the body combined with the faeces, neverthe- 

 less some is reabsorbed and excreted in the urine as urobilin. Some 

 observers state that intestinal micro-organisms can reduce bilirubin 

 to urobilin. 



UROCHROME is regarded as the proper pigment of the urine, giv- 

 ing to this secretion its familiar yellow color. When removed from 

 this medium the urine loses nearly all of its color. It is separable 

 into yellow scales. Urochrome may decompose to produce urome- 

 lanin, among other products. The last-named constituent gives a 

 blackish tinge to the urine. 



UROERYTHRIN. Aqueous solutions of urochrome, when exposed 

 to the air and so oxidized, turn red (uroerythrin). This coloring 

 matter is familiarly known by reason of its association with the acid 



