BODY TISSUES AND FLUIDS 443 



and 14 per cent for the amino-acid nitrogen, 28 per cent of the total non- 

 protein nitrogen still remains unaccounted for. With the rise in the urea 

 nitrogen that occurs in many cases of nephritis with marked nitrogen 

 retention there is a corresponding decline in the percentage of the rest 

 nitrogen, indicating that the actual amount of the rest nitrogen remains 

 fairly constant under abnormal conditions. As pointed out by Ham- 

 mett, there is, however, considerable variation in the amount of the rest 

 nitrogen of practically normal individuals. He found variations of 4 

 to 18 mg. with an average of 11 mg. to 100 c.c. in sixty cases. These 

 figures represent the difference between the non-protein nitrogen and the 

 sum total of the urea, uric acid, creatinin, creatin and amino-acid nitrogen. 

 While our methods are not sufficiently accurate to make the findings for 

 the rest nitrogen reliable, still they do indicate that this fraction is quite 

 large. At the present time we possess no very good information as to the 

 nature of this material in human blood, although it would seem possible 

 from the experimental work of Whipple and Van Slyke on proteose intoxi- 

 cation that a large part of this nitrogen was derived from peptids. From 

 the work of Abel we also have reason to believe that traces of proteoses are 

 present. 



Blood Sugar. A sugarlike substance was first recognized in the blood 

 in a case of diabetes by Dobson in 1775, but it was not until seventy years 

 later that its presence in normal blood was discovered by the noted French 

 physiologist, Claude Bernard. By means of his sugar piqure Bernard 

 first noted the connection between hyperglycemia and glycosuria (gly- 

 curesis). It remained for Lewis and Benedict in 1913 to introduce a 

 colorimetrie method for blood sugar estimation so simple that it could be 

 readily employed for clinical as well as scientific purposes. Earlier in the 

 same year Bang had described a very ingenious method requiring only 

 two to three drops of blood, but the fact that it was a gravimetric-volu- 

 metric procedure precluded any very extensive clinical application. Stimu- 

 lated by these methods, and several others since devised, many studies 

 dealing with the sugar of the blood have recently appeared. Previous to 

 the introduction of these simple methods, however, Bang (d) had written 

 a very interesting monograph under the title "Der Blutzucker," while 

 Macleod(&) had discussed the subject of diabetes almost entirely upon the 

 basis of experimental observations on the blood sugar. 



If we may rely upon the findings with the Benedict method, the blood 

 sugar of the normal human subject falls somewhere between 0.09 and 

 0.12 per cent, on the average being about 0.10 per cent. Depending upon 

 the method which is employed for the estimation, one may obtain figures 

 differing as much as 0.02 per cent in the normal bood, while with patho- 

 logical bloods the differences, as shown by Host and Hatlehol, may be 

 somewhat greater. Slightly higher figures appear to be obtained by the 

 picric acid method of Benedict in its various modifications than by most 



