A DETAILED METHOD FOR THE PREPARATION 
OF HISTIDINE. 
By HORRY M. JONES. 
(From the Psychopathic Laboratory of Cook County Hospital, Chicago.) 
(Received for publication, January 18, 1918.) 
The many uses which are being found for histidine in various 
lines of biological work and the difficulty of obtaining this amino- 
acid on the market make it necessary for many research labora- 
tories to prepare their own supplies of histidine. 
Directions for the preparation of histidine as given in the text- 
books are usually too meager to lead one to a successful first trial; 
z.e., a good yield and a pure product. Either a large amount of 
the product is discarded unawares in one of the precipitates or 
filtrates, or else the mother liquor is too grossly contaminated 
with other salts to permit the product to separate in pure crystals. 
The method given here is offered, however, not as an improve- 
ment on the method already in use, but as a more detailed state- 
ment of that method, together with reasons for certain apparently 
insignificant steps in the process which are easily overlooked. | 
Hemoglobin is the protein of preference as a source of histidine; 
and ox blood corpuscles, or the so called blood paste,! which can 
be obtained from the slaughter house, are probably the most eco- 
nomical source of histidine. 
2 liters of blood paste are placed in a wide-bottomed aR or 
porcelain-lined pan and to this is added ‘slowly an equal quantity 
of concentrated HCl. The lumping of the corpuscles into large 
masses is of no significance, as these lumps will dissolve later. 
The mixture is then poured into an 8 or 10 liter Jena or Pyrex 
round-bottomed flask and heated on a sand bath in the fume 
chamber for about 18 hours. By this time the volume of the 
mixture will be reduced to about half the original volume;:z.e., 
2 liters. The biuret test on a neutralized and filtered portion 
should now be negative. If the biuret test is negative, the flame 
1‘‘Blood paste”’ is the concentrated suspension of red blood corpuscles 
obtained by centrifugating defibrinated ox blood. 
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