Vol. 7, 1921 CHEMISTRY: VAN SLYKE AND HILLER 
185 
in Pliocene time; that these creatures represent the type of hyena bear 
most nearly approaching the Arctotheres and were widely distributed 
in North America. There is reason to believe that from this group the 
Arctotheres may have developed within the American region, and that 
the Arctotheres by way of a wide land bridge came to people South Amer- 
ica. 
The present spectacle bears of South America seem then to represent 
the last remnant of a group which originated in the Old World, was once 
widely distributed over the world, and included the largest of all known 
bears. 
AN UNIDENTIFIED BASE AMONG THE HYDROLYTIC PROD- 
UCTS OF GELATIN 
Donald D. Van Slyke and Alma Hiller 
Hospital of the Rockefeller Institute for Medical Research, New York, N. Y. 
Communicated June 25, 1921 
Of the known amino acids yielded by acid hydrolysis of proteins the 
work of various authors 1 has indicated that four, viz., histidine, arginine, 
lysine, and cystine, are distinguished from the others by the relative in- 
solubility of their phosphotungstates in acid solution. On the basis of 
this fact Van Slyke 1 devised a method for separating these four amino acids 
as phosphotungstates, and determining them by utilizing certain character- 
istics of their chemical structure. The non-amino nitrogen of this group 
of amino acids is entirely in the histidine and arginine. The arginine was 
determined directly, and the histidine was estimated on the assumption 
that all the remaining non-amino nitrogen was in histidine. 
This assumption we have tested by comparing the histidine content of 
a number of proteins as determined in the above manner with the values 
determined by Koessler and Hanke's direct colorimetric method. 2 In 
casein, edestin, and fibrin, the results by the two methods agree. But 
in gelatin the calculation based on the non-amino nitrogen indicates 6.1 
per cent of the total protein nitrogen in the form of histidine, while the 
colorimetric method shows only 1.8 per cent. There is evidently among 
the products of gelatin hydrolyzed by hydrochloric acid a substance, or 
substances, hitherto unrecognized, precipitated with phosphotungstic 
acid under the conditions ordinarily utilized to precipitate the hexone 
bases. 
In attempting to isolate the substance we have precipitated it by means 
of phosphotungstic acid with the other bases, have redissolved the pre- 
cipitate and freed it from phosphotungstic acid. The histidine and ar- 
ginine were removed by precipitation with silver sulfate and barium hy- 
