Nitrogen in Urine. 361 



specific gravity discussed on page 354 can best be interpreted. The proportion 

 of ash. in total solids is as a rule, greatest on the first day and markedly less 

 on the second day. In the longer fasts the proportion is relatively constant 

 after the second day, although in experiment No. 77, an unusually high 

 percentage of mineral matter was excreted on all four days. A ratio apparently 

 exists between the proportion of mineral matter shown in column i and the 

 relation between specific gravity and total solids as given in column h of the 

 table. The higher the percentage of ash in the total solids, the lower the ratios 

 shown in column h. This is especially noticeable in considering different days 

 of the same experiment, but does not obtain for different experiments even 

 with the same subject. In the shorter fasts the ratio between columns i and h 

 is more nearly uniform. Indeed, even from experiment to experiment and 

 with different subjects, the general rule may be noted that the higher the data 

 in column i, the lower the corresponding data of column h. Thus the highest 

 percentage of ash is 45 on the first day of experiment No. 80, and the lowest 

 relation observed in the shorter experiments was 2.2 on the same day. 

 Similarly, while the lowest percentages of ash occurred on the second days of 

 experiments Nos. 83, 85, and 89, the highest ratios of total solids to specific 

 gravity were observed on these days. These observations are fully in accord 

 with the well known fact that the density of solutions of sodium chloride (a 

 typical urine salt) is greater than that of solutions containing equal weights of 

 urea (a typical organic urinary constituent). 



NITROGEN. 



The elimination in the urine of the partially oxidized protein in the form 

 of a number of nitrogenous products has given to the determination of nitrogen 

 an especial significance. 



In all the earlier fasting experiments, the study of the nitrogenous ingre- 

 dients of the urine has received by far the greatest attention of any individual 

 factor. The collection and analysis of urine were comparatively simple matters, 

 while the analyses of the respiratory products were in general precluded. 

 Consequently we find in the literature of the subject a large number of deter- 

 minations of nitrogen in fasting urines which are of especial interest in 

 discussing the nitrogen elimination in the experiments here reported. 



Eecent investigations, notably those of Folin, have shown the importance of 

 determining not only the total nitrogen but also the different nitrogenous 

 ingredients, and of apportioning the nitrogen among these ingredients. In 

 earlier experiments, however, the partition of the total nitrogen was not 

 attempted and in the Middletown experiments here reported, it was impossible 

 to determine the nitrogenous compounds directly, except in the instances where 

 the determinations of creatine and creatinine, and a very few of uric acid, were 

 made. 



