192 EXCRETION. 



definite time than to learn simply their proportions in the 

 urine ; and in making out a table of the composition of the 

 urine, we will give, as far as possible, the absolute quantity 

 of its different constituents excreted in twenty-four hours. 

 This latter point, however, will be more elaborately consid- 

 ered in connection with the .characters of the individual 

 excrementitious principles and their variations under physio- 

 logical conditions. In compiling this table, we have taken 

 advantage of the elaborate bibliographical and experimental 

 researches of Prof. Robin, contained in his recent work upon 

 the humors, 1 but have made some changes and corrections 

 in his list of urinary constituents : 



1 ROBIN, Le$ ons sur les humeurs, Paris, 1867. In the table given by Robin 

 (p. 654), there is evidently a very serious error in one of the figures giving the 

 proportion of water. In quotations from this table in a very recent French 

 work on the chemistry of the urine, this error is corrected (BERGERET, De V urine, 

 Paris, 1868, pp. 13, 24). 



Although this table represents, very nearly, the latest and most reliable 

 observations upon the relative and absolute quantities of the urinary constitu- 

 ents, there are a few minor points that demand some explanation. For exam- 

 ple, Robin estimates the proportion of hippurates at a little less than the pro- 

 portion of urates, while many writers of high authority speak of the hippurates 

 as excreted in rather larger quantity (PARKES, TJie Composition of the Urine, 

 London, 1860, p. 13, and NEUBAUER AND VOGEL, A Guide to tlie Qualitative 

 and Quantitative Analysis of the Urine, London, 1863, p. 33) ; but the investi- 

 gations with regard to the daily excretion of hippuric acid have not been so 

 definite and satisfactory as those on which the estimates of the excretion of 

 uric acid are based. Robin gives, also, the proportion of creatine as 1*4 to 2 '6 

 parts per 1,000, and of creatinine, 0'2 to 0'4 per 1,000 ; and most authors give 

 in the urine a larger proportion of creatinine. This difference, however, is 

 not important, for, as far as the process of excretion is concerned, these two 

 substances may be regarded as a single principle ; creatine being readily con- 

 verted into creatinine in the urine by simple decomposition. In our endeavor to 

 make this table as complete as possible, we have reduced the figures given by 

 many authors to represent the amounts of uric acid, phosphoric acid, sulphuric 

 acid, chlorine, etc., to the quantity of the salts as they actually exist. This is 

 particularly important in a work on physiology, for chlorine and the various 

 acids just enumerated are not proximate constituents of the urine, except when 

 combined with bases. It is simply a matter of convenience to estimate them 

 separately, and the proportions of salts are readily calculated from the combin- 

 ing equivalents of the different elements. 



