442 VICTOR C. MYERS 



amount does not appear to be increased except in terminal nephritis with 

 marked nitrogen retention, when values as high as 30 mg. may be attained. 

 According to Hunter and Campbell (&) the average creatin content of the; 

 corpuscles lies roughly between 6 and 9 mg. per 100 c.c., while that of the 

 plasma is not more than 0.4 to 0.6, the blood as a whole containing about 3 

 mg., and slightly higher figures being found in females than males. Accord- 

 ing to these investigators there is a distinct correspondence between increase 

 of plasma creatin and the appearance of creatin in the urine ; but whether 

 the plasma, in the absence of creatinuria, is creatin-free or whether there 

 exists a threshold for creatin excretion, has not been positively determined. 



Amino-Acids. That the amino-acids formed in proteolytic digestion 

 are taken up directly by the blood was first clearly shown by Van Slyke 

 and Meyer (a), employing Van Slyke's method forthe determination. This 

 had been made probable from results obtained for the non-protein nitrogen 

 of the blood by Folin and Denis shortly before, but the work of Van Slyke 

 and Meyer conclusively proved this point, thus definitely settling one of 

 the long disputed questions of protein absorption. They found, for ex- 

 ample, that whereas the amino-acid nitrogen of a normal fasting dog 

 amounted to 4 to 5 mg. per 100 c.c. of blood, it was increased to 9 to 10 

 mg. after a heavy protein, meal. 



Comparatively few data are available for the amino-acid nitrogen con- 

 tent of human blood. The normal content of amino nitrogen may be given 

 a& 4 to 8 mg., with an average close to 5 mg., per 100 c.c. of blood. 

 In a series of sixty practically normal subjects Hammett (c) found 

 the amino nitrogen to be relatively constant with an average of 4.9 and 

 variations of 3.1 to 7.2 mg. per 100 c.c. of blood. Bock has reported anal- 

 yses on a series of miscellaneous pathological cases. He failed to find 

 any noteworthy deviations from the normal except in severe nephritis, 

 where in several cases figures exceeding 10 mg. and in one instance 30 

 mg. was reached. In' general the findings of Hammett and Bock harmon- 

 ize very well, though the figures of Hammett average slightly lower, pos- 

 sibly due to the fact that he used tungstic acid as the protein precipitant, 

 while Bock employed trichloracetic acid. 



Ammonia. According to the recent observations of Nash and Bene- 

 dict, the ammonia nitrogen content of the blood (of dogs and cats) under 

 normal and various experimental conditions is close to 0.1 mg. per 100 c.c. 

 They express the view that the urea of the blood is the probable precursor 

 of the urinary ammonia, and that the kidney is the seat of this trans- 

 formation. 



Rest Nitrogen. The amount of undetermined nitrogen present in 

 protein-free blood filtrates appears always to be very large. In the table on 

 page 434 the normal rest nitrogen was given as 45 per cent of the total 

 non-protein nitrogen. Here the creatin and amino-acid nitrogen were in- 

 cluded. If deductions of 4 per cent are made for the creatin nitrogen 



