428 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



phan has been suggested by Neumeister, 1 from the point of view that 

 it may be made to serve as an indicator of when tryptic digestion has 

 reached a certain stage and amido-acids are beginning to be formed,- since 

 it first appears in the more advanced stages of proteid decomposition simul- 

 taneously with the amido-acids. Tryptophan has never been isolated, and is 

 only known by its colour reactions. When not very dilute, the rose-red colour 

 is replaced by violet, and Kiihne has shown that the colour is given by 

 bromine water as well as by chlorine water. According to Krukenberg, 3 

 the colour is not due to oxidation by the chlorine or bromine, but to the 

 formation of an addition compound ; he also states that tryptophan is 

 slightly soluble in alcohol, ether, and chloroform. Hemala 4 has shown that 

 the coloured material is easily soluble in amyl alcohol. Here chlorine and not 

 bromine water must be used as a test, for the latter itself imparts colour to 

 amyl alcohol. When much peptone or Bother impurity is present with it in 

 solution, it falls, after some time, as a precipitate ; this on shaking up with 

 alcohol gives a fine violet solution showing an absorption band at the 

 D line. According to Krukenberg, a strong coloration is given even by 

 traces of the chromogen ; he also has shown that tryptophan is diffusible. 



In its reaction with bromine and chlorine water, tryptophan closely 

 resembles the chromogen of the suprarenal gland ; the two chromogens are 

 also alike in being diffusible and in their powerful tinctorial action, but here 

 resemblance ceases. The chromogen of suprarenals is very easily destroyed by 

 alkalies, could not be formed in pancreatic digestion, and is quite insoluble in 

 dry alcohol, ether, or chloroform. 



Kiihne has shown that tryptophan is a constant product in all proteid 

 decomposition, but that it is rapidly destroyed and disappears ; it is also 

 rapidly destroyed by putrefactive changes. 



When pancreatic digestion is accompanied by putrefaction, many other 

 substances are formed besides those above described. These will be considered 

 in connection with bacterial digestion in the intestine. 



DIGESTION OF VAKIOUS BODIES ALLIED TO THE PKOTEIDS. 



Those substances, such as the mucins and nucleo-proteids, which 

 consist of a proteid molecule united to some organic radicle (and called 

 Prote'ide by Hoppe-Seyler), first undergo a cleavage into proteid and the 

 body involved with it ; the proteid is then digested in the usual fashion, 

 while the other substance very often suffers no change. In this manner 

 haemoglobin is decomposed by peptic digestion into a proteid commonly 

 supposed to be a globulin, which becomes converted through albumose 

 into peptone, and hrematin. which remains unchanged. Nucleo-proteids 

 and nucleo-albumins 5 yield on similar treatment an insoluble residue 

 of nuclein, or of pseudo-nuclem or paranuclein respectively, and the 

 proteid part of the molecule is peptonised. In the tryptic digestion of 

 fibrin some of the xanthin bases (or nuclein bases) have been found ; 

 these arise from the breaking up of nuclear-nuclein (Kernnudein) 

 present as a constituent of admixed nucleo-proteid, derived from the 

 nuclei of white blood corpuscles. The nuclein breaks up into nucleic 



1 Ztsclir.f. Biol., Miinchcn, 1890, Bd, xxvii. S. 309. 



2 The name proteiiiochromogen has been given to this chromogen by Stadelmann, 

 ibid., 1890, Bd. xxvi. S. 491. 



3 Krukenberg, Virchow's Archiv, 1885, Bd. ci. S. 555; Verhandl. d. phys.-med. 

 Gesellsch. zu Wiirzburg, 1884, S. 179. 



4 Loc. cit. See also Neumeister, Ztsclir.f. Biol., Miinchen, 1890, Bd. xxvi. S. 332. 



5 Nucleo-proteids yield on decomposition a true nuclein, containing nucleic bases, 

 nucleo-albumins a pseudo-nuclem or paranuclein, which does not contain such bases. 



