Aveust 2, 1918] 
statements in his paper to which it seems 
worthy of calling attention. 
He states :1 
In the footings of the different analyses it will 
be noted that the 12-hour digestions give footings 
more than 2.5 per cent. over 100. In the 15-hour 
digestion the footing is good, while in the 24- and 
48-hour digestions the footings are 2.75 per cent. 
less than 100, thus indicating that the 12-hour ex- 
periments were probably not completely hydro- 
lyzed; whereas the 15-hour digestion was sufficient 
to bring about complete hydrolysis and the 24- and 
48-hour experiments were over-digested to the ex- 
tent that nitrogen was lost. 
One can but wonder where he secured such 
reasoning, or it is needless to point out that 
not more than 100 per cent. of the original ni- 
trogen can be present in a protein hydrolysate 
even if complete hydrolysis has not taken place 
and the literature of proteins shows that no ni- 
trogen is lost by overhydrolysis. Gortner 
and Holm‘ recently hydrolyzed fibrin for 6 
weeks and obtained a recovery of 99 per cent., 
while 201 hours’ hydrolysis showed a recovery 
of 100.7 per cent. the figures being, in both 
instances, within the experimental error of the 
analyses. 
However, his most astounding conclusion 
is that the nitrogen in the insoluble residue 
obtained from the casein starch digestion “ is 
in an inert form and its estimation should not 
be included in the humin determination,” with 
the result that he ignored the presence of ni- 
trogen in this fraction in calculating his nitro- 
gen distribution. Unfortunately he does not 
tell us how much nitrogen remained in this 
fraction® so that we can not recalculate his 
data, and as a result all of his laborious analy- 
ses are worthless. I use the word “ astound- 
ing” in the above sentence advisedly, for in 
all of the protein literature I can find no refer- 
ence to the black humin of protein hydrolysis 
which does not define it as insoluble, unre- 
active and inert, and any one who has studied 
its properties knows well that it is one of the 
4R. A. Gortner and G. E. Holm, J. Amer. Chem. 
Soc., Vol. 39, pp. 2736-2745 (1917). 
5 He does give the per cent. of nitrogen in the 
black material but not the weight of the black ma- 
terial. 
SCIENCE 
123 
least reactive of the chemical substances ordin- 
arily met with, resembling in much of its be- 
havior ordinary bone black. The humin of 
protein hydrolysis is a black, granular, non- 
crystalline substance, insoluble in the ordinary 
organic solvents, somewhat soluble in alkalis 
from which solution it is precipitated again by 
acids, and, in short, the true humin of protein 
hydrolysis agrees in every respect as regards 
physical properties with the material which 
McHargue discards and refuses to call humin. 
Then again, the nitrogen of the fraction 
which he discards certainly belonged to the 
original casein, for his starch was practically 
nitrogen-free. How then can he claim that 
hydrolysis in the presence of starch does not 
alter the nitrogen distribution? This nitro- 
gen which he discards belonged to the original 
protein molecule and should be included in the 
starch hydrolysates if it is included in the 
original casein analysis with which the starch 
hydrolysates are compared. 
As I have shown previously (2), hydrolysis 
in the presence of carbohydrates causes a very 
considerable increase in the insoluble humin 
fraction and this increase is due to both 
chemical and physical causes. The nitrogen 
in the true humin of a protein hydrolysate has 
its origin almost wholly in the tryptophane 
molecule® and the reaction by which it is 
formed appears to be the condensation of tryp- 
tophane with an aldehyde or ketone. When 
carbohydrates are present the acid causes the 
formation of furfural which condenses with 
the tryptophane to form a “humin.” How- 
ever, furfural itself has the peculiar property 
of polymerizing(?), in the presence of 20 per 
cent. hydrochloric acid, to a black insoluble 
substance with the result that a large mass 
of porous black material is formed in the hy- 
drolysate and this material, presumably 
through physical means, retains a very con- 
siderable amount of non-tryptophane nitrogen 
which normally would not appear in the humin 
fraction. Perhaps these latter forms of ni- 
trogen would not be present in the black mass 
formed from the furfural in as great a quan- 
éR. A. Gortner and G. E. Holm, J. Amer. Chem. 
Soc., Vol. 39, pp. 2477-2501 (1917). 
