454 Influence of Inanition on Metabolism. 



in the urine may have originated either in katabolized protein, purin bodies, 

 creatine and creatinine, or preformed urea and other crystallized end products 

 of katabolism, the only index of the total protein katabolism commonly used 

 is the total excretion of nitrogen. Contrary to the natural supposition, the 

 problem is most complicated in fasting experiments ; for although under ordi- 

 nary conditions with food the excretion of phosphorus and sulphur may be 

 significant of the breaking down of protein, during inanition the excretions of 

 nitrogen, sulphur, and phosphorus indicate profound disturbances in the 

 katabolism. 



A number of writers have attempted to compute the protein katabolized from 

 the sulphur elimination, by assuming that the sulphur content of protein is 

 relatively constant. The ratio of nitrogen to sulphur has been used in this 

 connection. But the wide variations in the amounts of sulphur present in the 

 various proteins existing in the body make it difficult to utilize with any degree 

 of satisfaction the data obtained from the sulphur and nitrogen determinations 

 and especially the ratio between them. Sherman 142 has computed the ratio 

 of nitrogen to sulphur in a large number of vegetable and animal proteins. 

 With the proteins of the body, the ratios range from 44.6 : 1 in oxy-hemoglobin 

 to 5:1 in tendon mucin and osseo-mucoid ; in myosin, serum globulin, and 

 fibrinogen, the ratios are more constant, namely, 13.1 : 1, 14.3 : 1, and 13.3 : 1, 

 respectively. 



It is commonly assumed that body protein contains from 16 to 17 per cent 

 of nitrogen, and since this percentage is not markedly different in the different 

 animal proteins, the assumption is reasonably well grounded; but as has been 

 shown above, the ratios of nitrogen to sulphur vary so widely as to practically 

 preclude any scientific deductions from them regarding the nature and amount 

 of the protein katabolized. The probability that there are at least two kinds 

 of protein katabolism occurring in the body, namely, exogenous and endo- 

 genous, justifies the belief that there is a noticeable difference in the sulphur 

 content of the two kinds of protein katabolized. While the nitrogen-sulphur 

 ratio in fibrinogen, serum globulin, and myosin is fairly constant and this 

 could properly be used if these were the only proteins katabolized, an examina- 

 tion of the ratios found in the experiments here reported (see table 209) shows 

 that on only one day was the nitrogen-sulphur ratio as low as 14.12, namely, 

 the fifth day of experiment No. 73. The ratios on all the other days were 

 considerably higher, averaging not far from 16.8. This fact clearly indicates 

 that material amounts of some form of protein with a lower sulphur content 

 than that of myosin, serum globulin, or fibrinogen, must have been katabolized. 

 Obviously, this ratio would be very much increased by an excretion of the 

 sulphur-free extractives. The output of total creatinine, from the results 

 obtained in these experiments (see table 203, p. 388) remains singularly con- 



U. S. Dept. Agr., Office of Expt. Sta. Bui. No. 121, p. 10. 



