408 THE ELIMINATION OF WASTE PRODUCTS. 



color. Some observers, on the other hand, maintain that normal urine does 

 contain and, in part at least, owes its normal color to a somewhat similar 

 but different body, which in consequence they have called " normal " uro- 

 bilin. It is in fact not possible, at the present moment, to make definite and 

 satisfactory statements as to whether urine contains one or more than one 

 normal pigment, as to its or their nature, as to whether they are derived 

 from bile pigment or directly from the hsernatin or haemoglobin or in other 

 ways, or as to the several steps by which they are produced. There are also 

 abnormal coloring matters present on occasion, such for instance as the pecu- 

 liar red coloring matter occurring sometimes in the urine of acute rheuma- 

 tism, which has been called uroerythrin ; but our knowledge concerning 

 these is very imperfect. 



341. Ferments and other bodies. Even normal urine has frequently 

 been found to contain a small quantity, hardly amounting to more than a 

 trace, of proteid material, apparently an albumin ; but the normal presence 

 of even this small quantity has been disputed. Urine, however, certainly 

 contains ferment bodies. 



When urine is treated with many times its volume of alcohol, a granular 

 or flocculent precipitate is thrown down, consisting chiefly of phosphates, 

 together with some other substances or probably several other substances, in 

 very small quantities. An aqueous solution of the precipitate, which may 

 be freed from the phosphates, is both amylolytic and proteolytic. Ferments 

 may also and more readily be extracted from urine by allowing shreds of 

 fibrin to soak in the urine for a few hours, and then removing and washing 

 them. The ferments become entangled in the fibrin in such a way as not 

 to be easily removed by washing. The washed shreds will convert starch 

 into sugar; and when treated with dilute hydrochloric acid digest them- 

 selves, showing the presence of pepsin. By this method it has been ascer- 

 tained that an amylolytic ferment and pepsin are present in quantities which' 

 vary in the twenty-four hours according to the meals. Rennin has also been 

 found, and, at times at least, trypsin. From this it appears that some of the 

 ferments of the alimentary canal escape from the body by the urine, being 

 probably reabsorbed directly from the respective gland ; the quantity which 

 thus escapes is insignificant. 



A small quantity of gas, about 15 vols. per cent., can be extracted by the 

 mercurial pump from urine received direct from the body without exposure 

 to air. The gas so obtained consists chiefly of carbonic acid, nitrogen being 

 very scanty, and oxygen occurring in very small quantities or being wholly 

 absent. The meaning of this we have already touched upon in speaking of 

 respiration (see 302). 



342. The quantities in which these multifarious bodies, all of which, 

 as we have seen, we may perhaps regard as constituents of normal urine, are 

 present in different specimens of urine, vary within very wide limits, being 

 dependent on the nature of the food taken and on the conditions of the body. 

 The amount not of water only, but of many of the other several constituents, 

 varies widely and indeed rapidly, so that the percentage composition of urine 

 will vary from hour to hour if not from minute to minute. The causes which 

 determine these variations in the nature and amount of urine we shall study 

 later on. Meanwhile what may be called the average composition of human 

 urine is shown in the following table in which the acids and bases are put down 

 separately. 



