520 COMPOSITION OF URINE. [BOOK n. 



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 wash- 

 ing. The washed shreds will convert starch into sugar ; and 

 when treated with dilute hydrochloric acid digest themselves, 

 shewing the presence of pepsin. By this method it has been 

 ascertained that an amylolytic ferment and pepsin are present in 

 quantities which vary in the twenty-four hours according to the 

 meals. Eennin has also been found, and at times at least, tryp- 

 sin. From this it appears that some of the ferments of the ali- 

 mentary canal escape from the body by the urine, being probably 

 re-absorbed directly from the respective glands ; the quantity 

 moreover which thus escapes is insignificant. 



A small quantity of gas, about 15 vols. p.c., 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 290. 



326. The quantities in which these multifarious bodies, 

 all of which as we have seen we may perhaps regard as con- 

 stituents 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 per- 

 centage composition of urine will vary from hour to hour if not 

 from minute to minute. The causes which determine these vari- 

 ations in the nature and amount of urine we shall study later on. 

 Meanwhile what may be called the average composition of 

 human urine is shewn in the following table in which the acids 

 and bases are put down separately. 



AMOUNTS OF THE SEVERAL URINARY CONSTITUENTS PASSED 

 IN TWENTY-FOUR HOURS. (After PARKES.) 



By an average Per 1 kilo 



man of 66 kilos. of body weight. 



Water 1500-000 grammes 23-0000 grammes 



Total Solids 1-1000 



Urea 33-180 -5000 



Uric Acid -555 -0084 



Hippuric Acid -400 -0060 



Kreatinin -910 -0140 

 Pigment, and 



other substances 10-000 -1510 



