CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 653 



trypsin. From this it appears that some of the ferments of the 

 alimentary 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 

 359. 



406. 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 com- 

 position 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 

 shewn in the following table in which "the acids and bases are 

 put down separately. 



AMOUNTS OF THE SEVEEAL UKINAKY CONSTITUENTS PASSED 

 IN TWENTY-FOUR HOUES. (After PAKKES.) 



By an average Per 1 kilo 



man of 66 kilos. of body weight. 



Water 1500*000 grammes 23*0000 grammes 



Total Solids 11000 



Urea 33180 -5000 



Uric Acid '555 -0084 



Hippuric Acid '400 '0060 



Kreatinin '910 -0140 



Pigment, and 



other substances 10*000 1510 



Sulphuric Acid 2'012 -0305 



Phosphoric Acid 3164 '0480 



Chlorine 7*000 1260 



(8*21) 



Ammonia 770 



Potassium 2*500 



Sodium 11*090 



Calcium -260 



Magnesium '207 



72*000 



