134 



SCIENCE. 



[N. S. Vol. XXII. No. 553. 



from which Curtius has made the deriva- 

 tives referred to above. In the same connec- 

 tion Fischer explained that a similar reac- 

 tion follows with the anhydrides of alanine 

 and leucine, from M^hich alanylalanine and 

 leucylleucine must result. To carry the 

 process farther and obtain more complex 

 groups proved practically difficult. An- 

 other method was finally developed which 

 may be illustrated by some of the simplest 

 cases described by Fischer. On bringing 

 together a halogen acid chloride, for ex- 

 ample chloraeetyl chloride, with an ester 

 of glycylglycine, chloracetylglycylglycine 

 ester results, 



CICILCO . NHCH.CO . NHCHoCOOC.Hs, 



which on saponification yields the acid. 

 The latter in turn when treated with 

 strong ammonia gives up chlorine for the 

 amino group and diglycylglycine results. 

 "With a-brompropionyl bromide employed 

 as the halogen compound, alanylglycylgly- 

 cine is obtained, and with a-bromisocapro- 

 nyl chloride leucylglycylglycine is sejsured 

 in the same manner. 



It will be seen that while the processes 

 of Fischer and Curtius follow different 

 lines they lead usually to the same ends. 

 A considerable number of the Curtius in- 

 vestigations have been published in Vol. 70, 

 N. F., 1904, of the Jour, prakt. Chem. 

 under the title of 'Condensations of 

 Amido Acids,' while the Fischer work has 

 come out in recent volumes of the Berichte 

 under the general title of ' Syntheses of the 

 Polypeptides.' This work seems to be 

 more directly concerned with the building 

 up of bodies of physiological interest; the 

 Curtius work is somewhat more general. 

 Of many of the Fischer compounds it has 

 been shown that ready hydrolysis with ac- 

 tive pancreatic juice follows. The biuret 

 reaction is also given in many cases, but 

 apparently not always. Groups containing 

 tyrosine, cystin, leucine, alanine, etc., have 



been split by the ferments, and these, it will 

 be remembered, are among the most impor- 

 tant of the fractions secured by the hydrol- 

 ysis of the true proteins. The method of 

 producing these polypeptides seems to be 

 without limit and doubtless much more 

 complex aggregations will be secured. 

 Molecular weights of over 500 have already 

 been reached. 



Closely related to the qiiestion of the syn- 

 thesis of the polypeptides is that of the 

 composition of the simplest proteins. The 

 work of Kossel and others in this direction 

 has furnished most interesting results. 

 For several of the protamines and histones 

 the content of hexone bases has been found 

 with a fair degree of accuracy, and of 

 many of the more complex proteins the 

 amounts of both mono- and diamino acids 

 present have been found. The numbers 

 secured must be looked upon, however, as 

 minimum values because of the practical 

 difficulties in the way of quantitative sepa- 

 ration and identification. 



Several improved processes have been de- 

 veloped for the separation of amino acids 

 from digestion or other mixtures. A 

 method first suggested by Curtius for the 

 production of ethyl esters of the amino 

 acids, and which has been referred to above, 

 has been perfected by Fischer. From mix- 

 tures the esters are distilled off under 

 greatly reduced pressure. From the distil- 

 late some are separated by solvents, while 

 others, after conversion to acids, are sepa- 

 rated by fractional crystallization. It has 

 been found that y8-naphthalene sulphochlo- 

 ride combines with many of the amino acids 

 to form compounds of very slight solubility 

 and Fischer and Bergell have developed a 

 method of separation based on this fact. 

 Both general methods have been applied 

 also in the detection and estimation of 

 amino acids in urine which is likely to be- 

 come a matter of considerable clinical in- 



