BY DR. LAUDER BRUNTON. 531 



cream, added to 100 c. c. of water, were sufficient to form a mix- 

 ture which quite obscured a candle flame. When 8 c. c. are 

 required, the milk contains about 30 per cent, more water than 

 it ought to do, either from the addition of water, or of creamed 

 milk. When 12 c. c. are necessary, the milk contains 50 per 

 cent, too much water. 



THE URINE. 



** 181. Characters of Urine. The healthy urine of man 

 is a clear liquid of a golden color, possessed of a characteristic 

 odor, and having a specific gravity which generally varies from 

 1018 to 1023, although it may sink as low as 1005, or rise, under 

 opposite circumstances, as high as 1030. 



The reaction of the mixed urine of man under normal circum- - 

 stances is acid. l>y the term mixed urine, we understand a ^ 

 mixture of the different portions of urine passed during twenty- 

 four hours. 



When urine is allowed to stand for some hours, it deposits a - 

 slight cloudy sediment, which is called the mucous cloud, Midi '' 

 which consists of mucus holding in suspension a few epithelial 

 cells, derived from the genito-urinary passages. It is usually 

 affirmed that the urine, on exposure to the air, in clean vessels, 

 becomes, after some hours, much more acid than it was when 

 passed. To this change the name of the acid fermentation has 

 been given. There are no facts which prove the constant occur- 

 rence of this acid change. ^ When the urine is, however, placed 

 for periods which vary very greatly, in open vessels, exposed to 

 air, it ultimately invariably undergoes the so-called alkaline 



fermentation, i. e., its reaction becomes exceedingly alkaline, it / , , 

 emits an ammoniacal odor, and it becomes turbid, in conse-/ foi&rA 

 quence of the precipitation of phosphate of magnesium and am- 

 monium, of phosphate of calcium, and unite of ammonium. 



The acid reaction of healthy human urine is probably due, in ic _ 

 great part, to free carbonic acid, to uric and to hippuric acids ; 

 it has been commonly believed, however, that acid pli'osijhaje > &* 

 .of sodium exists in urine., and that the acidity of the fluid is 

 chiefly dne to its presence. 



The alkaline reaction of urine which has become decom- 

 posed is undoubtedly due to carbonate of ammonium. Un- 

 der the influence of putrescent animal substances it may be 

 observed that perfectly fresh urine becomes, in the course of 

 an hour or two, intensely fcetid. Under these circumstances, 

 the urea contained in urine combines with the elements of 

 water and is transformed into ammonium carbonate CH 4 N 2 + 

 H a O = (NH 4 ) 9 C0 3 . The following experiments throw much 

 light on the proximate causes of the alkaline fermentation of 

 urine: 



