428 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 
plian has been suggested by Xeumeister, 1 from tbe point of view tbat 
it may be made to serve as an indicator of when trj r ptic 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 other 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, coidd 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 Various Bodies allied to the Peoteids. 
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 
lucmoglobin is decomposed by peptic digestion into a proteid commonly 
supposed to be a globulin, which becomes converted through albumose 
isto peptone, and hsematin which remains unchanged. Nucleo-proteids 
and nucleo-albumms 5 yield on similar treatment an insoluble residue 
of nuclein, or of pseudo-nuclein 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 (Kern n/ucl 'ria) 
present as a constituent of admixed nucleo-proteid, derived from the 
nuclei of white blood corpuscles. The nuclein breaks up into nucleic 
1 Ztschr.f. Biol., Miinchen, 1890. Bd. xxvii. S. 309. 
2 The name proteinochromogen has been given to this chromogen by Stadelmann, 
ibid., 1S90, Bd. xxvi. S. 491. 
3 Krukenberg, Virehoiv's Arcliiv, 1885, Bd. ci. S. 555; Verhandl. d. phys.-med. 
Gesellsch. zu Wurzburg, 1884, S. 179. 
4 Loc. cit. See also Neumeister, Ztschr.f. Biol., Miinchen, 1S90, Bd. xxvi. S. 332. 
5 Nucleo-proteids yield on decomposition a true nuclein, containing nucleic bases, 
nucleo-albumins a pseudo-nuclein or paranuclein, which does not contain such bases. 
