Quality of Protein and Pellagra




CHAPTER X

THE QUALITY OF PROTEIN AND PELLAGRA

The protein
constituent of the food differs from all the others by its endless variety.
Egg-white and meat protein are quite distinct proteins. Milk contains two kinds
of protein: the casein which is used to make cheese, and an albumin, like
egg-albumin, in the whey. The presence of protein in cereals is obscured by
starch, yet about one-tenth of wheat flour is protein; in fact, two very
special proteins are present: gliadin, soluble in alcohol; and glutenin,
insoluble in alcohol but soluble in dilute alkali.

The proteins are classified by their physical differences, such as their
solubility in different solvents, heat coagula­tion, etc. It is not as yet
possible to classify them accord­ing to their chemical analysis, which is very
difficult and is still incomplete.

The work of Fischer, Kossel and their pupils has shown that proteins on
hydrolysis, i. e. by boiling with strong mineral acids, break down into
about twenty different amino acids. These units can be arranged in eight groups
according to their chemical nature:

(i)
Simple Mono-amino Acids.

Glycine, alanine, valine, leucine and iso-leucine.

(2)       

Mono-amino-dibasic
Acids.
Aspartic acid and glutamic acid.

(3)       

Hydroxy-amino Acids. Serine and hydroxyglutamic acid.

(4)       

Heterocyclic
Acids.
Proline and hydroxyproline.

100



QUALITY
OF PROTEIN AND PELLAGRA^' -lbl''

(5)       

Mono-amino Acids with
Aromatic Nucleus.
Phenylalanine and
tyrosine.

(6)       

Mono-amino Acid with
Indole Nucleus.
Tryptophan.

(7)       

Hexone Bases or Diamino
Acids.
Lysine, arginine and histidine.

(8)       

Thio-amino Acid. Gystine.

The chemical analysis of the protein shows that the various proteins
yield different amounts of the amino acids. Some of the data are shown in the
following table; the peculiarities of each protein are indicated by the figures
in heavy type :

 

 

 

O a

3

4

4

*3 U

it

I

If f I

A

11

4

a

55

Glycine  
....

2-1

0

0

19-3

0

09

0

0-3

3-8

 

Alanine   .

 

 

 

3-7

1-5

?25

30

3-0

4?

9-8

 

3-6

 

Valine     .

 

 

 

o-8

7-2

0-9

 

3-4

0-3

1-9

 

+

 

Leacine   . t

 

 

 

n-7

9-4

19'4

6-8

6-6

6-o

19*6

6-2

30-9

 

Phenylalanine

 

 

 

3-2

3-a

2-«

I'O

2-4

20

6-6

 

3-i

 

Tyrosine
.

 

 

 

2.2

4-5

0-9

0

1-2

4-3

3-6

3-8

2-1

 

Serine

 

 

 

 

o-5

 

0-4

0-2

°?

I-O

 

0-3

 

Cystine    .

 

 

 

 

 

 

0

o-J

 

 

 

0-3

 

Proline

 

 

 

5-8

6-7

4-0

10-4

13-2

4-2

9.0

J-o

4-1

 

Hydroxyproline

 

 

 

 

0.3

 

64

 

 

 

 

2-0

 

Aspartic Acid

 

 

 

4'3

1-4

I-O

1-2

o-6

0-9

1-7

0-7

4'5

 

Glutamic Acid

 

 

 

iJ-5

15-6

IO-I

1-8

43-7

234

288

12-7

18-7

 

Tryptophan

 

 

 

+

i-5

 

0

I-O

+

0

+

,t.

 

Arginine
.

 

 

 

7-5

3-8

Pz

9-3

3-2

4-7

16

7-1

14-4

68-2

Lysine

 

 

 

7-6

6-o

J-o

0-2        1-9

0

30

i-7

12-0

Histidine

i-8

3-5

2-1

0-4

0-6     i-8

o-8

3-0

2-4     
13-9

In general, the albumin group of proteins contains all the amino acids,
except glycine, in various proportions. The globulin group is similar, but
contains glycine, and has, in addition, a higher amount of glutamic acid, especially
those globulins of vegetable origin. The phosphoproteins (casein) resemble the
albumins, with no striking preponderance of any single amino acid. The gliadin
group of cereal proteins is peculiar in its high content of glutamic acid and
proline. Sturin, the protein of fish sperm, is made up of the three hexone
bases



Itig'
VITAMINS AND THE CHOICE OF FOOD

with
no, or very little, mono-amino acids. Gelatin lacks cystine, tyrosine and
tryptophan. These are merely some of the most obvious differences. Proteins
thus differ markedly in quality.

Our analytical data are far from complete; in no case do the totals of
the amino acids add up to ioo. The incompleteness is chiefly due to the great
difficulty of separating and estimating the individual amino acids. There may
be still some unknown amino acids in small quantities; e.g. hydroxyglutamic
acid has been dis­covered recently by Dakin by a new extraction method. This
method may lead to further discoveries; once again it has proved that every new
process in connection with the chemistry of the proteins has given a valuable
result.

The work of Fischer and Kossel has also revolutionised our conception of
protein metabolism. We no longer think, like Liebig and others, that the
protein of the food becomes directly the protein of the body, for it has been
demonstrated by physiologists that the protein of the food is split up during
digestion into its constituent amino acids, that the amino acids circulate in
the blood, and that the tissues select the amino acids from which their protein
is built up. All proteins are digestible by man except the scleroproteins, such
as horn, hair, silk, etc., which are therefore useless as food.

Differences in proteins may be due not only to a varia­tion in the
relative amounts of the amino acids which they contain, but also to differences
in the manner in which they are arranged. The protein molecule may be pictured
as a continuous chain of amino acids coiled upon itself. This method of
combination allows theoretically of endless variation; if only three amino
acids are taken they can be arranged in six different ways:

a-b-c,
b-a-c, c-b-a, a-c-b, b-c-a, c-a-b.

With eighteen or twenty amino acids the number of arrangements is almost
infinite. Two proteins may con­tain exactly similar amounts of amino acids and
yet be



QUALITY
OF PROTEIN AND  PELLAGRA     103

distinct
because of a difference in the sequence in which the amino acids are connected.
On this basis the difference which exists between the blood and milk proteins
of various species of mammals may perhaps be explained.

All
the amino acids are required by the animal body for building up its various
tissues, but with the exception of glycine, the simplest unit, and possibly of
proline, the amino acids cannot be formed in the animal organism, which is
therefore ultimately dependent upon the vegetable world for its protein supply.
Our animal food is derived from the grass eaten by cattle. The plant proteins
dur­ing digestion are split up into the various amino acids and built up into
proteins of quite different pattern; that is, containing amino acids in
different proportions and sequence. During this reconstructive process there
may be great waste of some amino acids. For example, if the protein of
ox-muscle, which contains about 16 per cent. of glutamic acid, has to be built
up from food in which the only protein is wheat gliadin, containing over 40 per
cent. of glutamic acid, there is a large waste of glutamic acid. Further, the
muscle protein requires about 8 per cent, of lysine for its construction, but
gliadin contains only 0-2 per cent, of lysine. In order to obtain sufficient
lysine, 40 parts of gliadin are required to construct one part of muscle
protein, so that the waste of glutamic acid is again increased. Cannibalism is
thus the most economical method of nutrition, as for each part of muscle protein
in the food it is theoretically possible to build up one part of muscle protein
in the body. The nearest parallel that there is to cannibalism is the nursing
of the infant by its mother. In general, for the building of muscle protein,
the flesh of animals is the best food.

Proteins can thus be classed as good, poor or incom­plete for
nutritional purposes. The good proteins are those which are converted with
little waste of amino acids into the body proteins. The poor proteins contain
all the amino acids, but in unsuitable proportions involving much waste of
certain amino acids. The incomplete proteins, such as



104   VITAMINS AND THE CHOICE OF
FOOD

gelatin
and zein, do not contain all the essential amino acids (see table, p. 101).

The proteins of speeds, including cereal grains, are gener­ally speaking
poor proteins, as they contain unsuitable proportions of the amino acids. The
proteins of green leaves, owing to difficulties in the way of chemical manipu­lation,
have not yet been analysed. Herbivorous animals live naturally on a diet in
which the protein is derived practically entirely from green leaves with a
small pro­portion of seeds. There is a record, though this can scarcely be
considered scientific evidence, that Roman

soldiers sometimes lived on a diet of peas and
cresses, that is, of leaf and seed. The digestive systems of man, pigs and
carnivores are not adapted for dealing with a bulk of material containing
cellulose, such as the herbivores eat. So-called vegetarians usually indulge in
some animal protein, e. g. milk, cheese, or eggs, but a truly vegetarian
diet may suffice if it is rightly selected as to its amino-acid content and is
not too bulky. Mixtures of seed, nut and leaf proteins may contain all the
essential amino acids in sufficient amount. It is the excessive preponderance
of proteins derived from cereals or seeds alone which constitute a dangerous
diet likely to produce pellagra.

The function of any individual amino acid may not be limited to its
share in building up tissue protein, it may play some part in the vital
processes; e.g. the iodine of the thyroid is present as an indole
compound, and the amino-acid tryptophan, an indole derivative, may be
indispensable for the maintenance of the thyroid function. In the same way
tyrosine or phenylalanine seem to be necessary for the formation of adrenaline
by the suprarenal glands.

The biological effect of the individual amino acids can only be tested
by feeding experiments. The practical difficulties of feeding animals with a
mixture of pure amino acids are far too great, because of the labour involved
in their preparation.    The plan adopted
is to feed



QUALITY OF PROTEIN AND PELLAGRA    
105

the
proteins which are known to be lacking in certain amino acids and compare the
result with the feeding of the same food plus the missing unit»or units.

The first experiment of this kind was made by Hopkins and Wilcock in
1906. They selected zein (from maize) as protein, which was amplified with the
addition of 2 per cent, of its amount of tryptophan. Young mice on the zein
alone immediately began to lose weight and generally died in 16 days; decline
in weight also occurred in another set with added tryptophan, but death did not
occur until the 30th day. Adult mice lived 27 days
,' without tryptophan, and 49 days with
tryptophan. Tryptophan had thus an appreciable effect on the sur­vival period
of the animals, but as zein is incomplete in respect of other units, the
addition of tryptophan alone was not sufficient to maintain normal life.

The experiment was repeated by Ackroyd and Hopkins under better
conditions. The amino-acid supply was derived from casein in which the
tryptophan had been destroyed by acid hydrolysis, but the mixture contained all
the other units. Tryptophan was at first added to the mixture, but omitted
after the twelfth day and included once more on the thirty-fifth day. There was
growth during the first period, decline in weight during the second period,
followed by growth on inclusion once more of the tryptophan. This is shown by
the continuous lines in Fig. 20. The upper dotted line shows continuous growth
on the complete mixture; the lower dotted line shows loss of weight in the
absence of tryptophan.

Similar experiments made by Osborne and Mendel in America on young rats
showed that zein produced growth if supplemented by tryptophan and lysine, but
even then the growth was not entirely satisfactory. These workers also tested
on growing rats the effect of wheat gliadin as sole source of protein; it
contains all the amino acids, but some of them, particularly lysine, are only
present in very small proportions. Adult rats were maintained for quite long periods,
as long as 500 days,



106   VITAMINS AND THE CHOICE OF FOOD

4
but young rats fed on gliadin lived but
did not grow. The growth impulse was not destroyed but remained dormant; if the
diet was changed to natural food at an

Grams

Fig. 20.—Weight
charts of rats showing the effe<it of withdrawing tryptophan from the diet
(Ackroyd and Hopkins). Ascending dotted line shows the average growth of 16
rats on complete amino acid mixture. Lower and descending dotted line sfcows
the average loss of 8 rats on diet without trytophan. Continuous lines show
average weight of 2 rats in each case. Tryptophan was removed on 12th day and
restored on 35th day.

Reproduced by kind permission from the Biochemical
Journal,
1916,10, 562.

age at which growth had normally ceased, the improved
diet caused the resumption of growth until full adult
size was reached.                  "

In
later experiments lysine was added at intervals and growth took place during
the periods in which lysine



 



Fig. 22.—Chickens
on grain mixture of high lysine content.

Fig. 23.—Chickens on grain
mixture of low lysine content.   
Chickens in both figures of same age (Buckner, Nollau and Kastle).

Reproduced
by kind permission from Bulletin No. 197, Kentucky Agricultural Experimental

Station, 1916.



QUALITY
OF PROTEIN ANft PELLAGRA     107

?
was given, but not in the periods without it; «the effect is clearly shown by
the weight charts, Fig. 21.

The effect of lysine upon growth has also been demon­strated by Buckner,
Nollau and Kastle in the case of chickens living under the natural conditions
of a poultry farm. Birds were fed upon grain mixtures of high or low lysine
content, and, as their photographs show (Figs. 22 and 23), more rapid growth
took place on the mixture of high lysine content.

Those proteins which are naturally
concerned with the

Fig. 21.—Weight charts of
rats showing indispensability of lysine for growth (Osborne and Mendel).

Reproduced by kind permission from Journal of
Biological Chemistry
(Baltimore),
,     1914,17, 342.

growth
of young animals, such as casein and lactalbumin in milk and vitellin in eggs,
all show a relatively high content of lysine, while it is entirely absent from
some vegetable proteins, such as hordein from barley and zein from maize.

No amount of energy value, nor of protein, in the food, however
abundant, can induce growth in young rats unless lysine be present. It is thus
useless to emphasise, as Rubner and others have done, the quantitative aspect
of the protein requirement for growth unless the quality of the protein is kept
clearly in mind.

The element sulphur is present in
proteins in the amino-



108   VITAMINS ANt)  THE 
CHOICE 
OF FOOD

acid
cystine, though it is possible that other sulphur-containing units may be
present. If a protein contains very little cystine, it will not produce normal
growth. Phaseolin, the chief protein of the haricot bean, is deficient in
cystine; kafirin, a protein from millet, is deficient in cystine and lysine;
casein is also poor in cystine.

In addition to tryptophan, lysine and cystine, the ammo acids, tyrosine
and phenylalanine, containing aromatic nuclei are probably also essential. The
di-amino acids, histidine and arginine, appear to be inter­related in
nutrition; absence of both causes loss of weight, but absence of either alone merely lessens the rate of growth. The
function of each individual amino acid has not yet been determined, and it is
not yet known if they are all indispensable.

The proportional amounts of the amino acids in any given protein are
constant and invariable. There is, for example, no evidence to suggest that the
cystine content of casein could be increased by feeding extra cystine to the
lactating animal.

Poor protein foods, such as maize meal, can for practical purposes be turned
into an efficient protein mixture by adding an equal weight of milk. A great
deal of useful work is being done to determine which are good proteins and to
find the most practical method of supplementing poor ones. The proteins of
cereals, on account of their extensive use as food for man and beast, have been
the centre of interest. At first sight it seems strange, if pellagra be
produced by a diet low in animal protein and rich in cereal, that there should
be no pellagra associated with a beri-beri producing diet of white polished
rice with little meat, the staple diet of so many millions in the East. An
investigation of the chemical nature of rice protein has shown that it more
closely resembles an animal protein in its amino acid make-up than does any
other cereal protein. In this connection words spoken by Hop­kins as long ago as 1907 have acquired an
almost prophetic value : " This matter of qualitative differences of
proteins



QUALITY OF PROTEIN AN* PELLAGRA     109

may
be of no small significance in dietaries. • It may account for what I believe
is proved by experience— that rice may serve the races which rely on it as an
almbst exclusive source of protein, while wheat is only suitable for races
which take a much more varied dietary."

Rice contains better protein than wheat, and wheat better than maize.
The relation of maize to pellagra, which for so long was inexplicable, now
becomes clear. Pellagra follows the deprivation of certain amino acids which
are not supplied in sufficient amount by maize. It does not develop if, in
addition to maize, there is present in the food some protein which suitably
supplements the deficiencies of the maize. Pellagra develops upon a diet
containing insufficient good protein even if no maize be eaten. Pellagra may
develop in spite of good protein in the food if any diseased condition of the
diges­tive tract prevents the digestion and assimilation of protein, e. g. after
dysentery or after certain operations.

It is not yet determined which of the amino acids are essential for the
prevention of pellagra, but as tryptophan, lysine, cystine and other amino
acids are indispensable for the formation of tissues, it is possible that the
deficiency of any one of them is a factor in the development of the disease.
The varying forms in which pellagra manifests itself may be accounted for by
the supposition that in one case the deficiency of tryptophan may be the
greatest, while in other cases cystine or lysine, etc., may be more deficient
than tryptophan, the diet of no two pellagrins being exactly similar in their
amino-acid content.

Chick and Hume (1920) carried out experiments on three monkeys to
determine the effect on them of pro­longed feeding with a diet of poor protein.
The three vitamins were given in ample amount and the energy value of the food
was sufficient. About 70 per cent, of the total protein consisted of zein, i.
e.
of maize protein; the diet was therefore known to be deficient in
tryptophan and lysine. After periods of 49, 
51 and 117 days respectively, all three monkeys



110   VITAMINS AND  THE CHOICE 
OF FOOD

developed
bi-laterally symmetrical skin eruptions resembling pellagra in man. The animals
lost weight slowly, became weak and ill, but only one had diarrhoea, and none
showed the nervous symptoms associated with pellagra. The addition of
tryptophan to the food, if given in time, improved the general condition, but
weight was not regained. The further addition of a mixture of lysine, histidine
and arginine had no marked effect. The daily addition of 5 to 10 grams of
plasmon (= casein) caused the skin lesions to disappear, but lost weight was
not regained until a normal diet of rice, wheat germ, milk and cabbage was
given. The experiment is of significance as it offers additional evidence that
a condition resembling pellagra is produced by a diet containing protein poor
in quality.

Besides the feeding of diets varying in amino-acid content there is
another practical method of determining the biological value of a protein. In
this method the amino-acid composition is
not considered, but its efficiency
is estimated by determining the least
quantity of a given protein which is required daily to keep an average man of 70 kilos, from loss of body weight; that is,
in nitrogenous
equilibrium. This method was first employed by Karl
Thomas in 1909, and from the results he obtained by feed­ing experiments on
himself, he was able to make a com­parative table of the biological value (=
B.P.V.) of the proteins in common food-stuffs. Milk protein was taken as the
standard and assigned a value of 100.

Smallest Daily Amount to Protect a Man
of 70 kilos, from loss of Body Weight   Grams.           B.
P.
V.

Beef    ..... 30      104

Milk    ..... 31      100

Fish.................................... 33         94

Rice................................... 34         88

Potato                                  
?    37           79

Pulse
(pea or bean)        .        .     54           55

Wheat          ..... 76     39

Maize ..... 102        29

The figures assigned by Thomas are only an approxima­tion and their
practical value has been questioned. Wilson, who has studied the diets
associated with pellagra



QUALITY OF
PROTEIN AND PELLAGRA     111

in
Egypt,
has found a calculation of the biological value of the protein by Thomas's
method to be a reliable guide. It is obvious that a diet containing a
sufficient amount of protein, according to the ioo grams standard (p. 10), is
physiologically inefficient if the protein is derived almost entirely from
cereals such as maize.

In order to estimate approximately the B.P.V. of a mixed diet the total
quantity of each protein must be divided by a factor; the factors used by Wilson were:—

 

Tor Animal

protein

.   
ro

   Rice

.        .        .

.     I-I2

   Potato

...

.    1-27

,,   Pulse

...

.     1-82

   Wheat

...

    2-55

   Maize

   
3-4

In planning a diet the minimum requirement should not be approximated
too closely. For instance, the 30 grams of animal protein daily, which are
sufficient under the favourable conditions of a laboratory experi­ment, are
probably insufficient under the changing conditions of ordinary life. These
minimal protein quantities only suffice if the rest of the diet is of proper
Calorie value. Individual variations must also be borne in mind when planning a
dietary for a large number of people; a diet sufficient in protein for the
majority might be deficient for some individuals. Wilson advises that the protein should have a
biological value equal to at least 40 grams of animal protein.

On these principles Wilson has proved
that the out­breaks of pellagra in refugee and prisoners' camps in Egypt were due
to a poor protein diet. The diet of Turkish prisoners of war doing no labour
had a B.P.V. of 38-6; those on moderate labour 48-2. There were more cases of
pellagra amongst the labour group in spite of their diet of better B.P.V.; the
effect of work upon the protein requirements is 
thus  indicated.    The 
same  effect  of



112   VITAMINS AND THE CHOICE OF FOOD

muscular
work was observed amongst Egyptian civilian prisoners. Convicts at hard labour
with a diet higher in B.P.V. than that of convicts on moderate or no labour yet
suffered more frequently from pellagra. Labour is thus a factor in the
causation of pellagra in a community where the good protein supply is on the
border of insuffi­ciency. Defective absorption, brought about by faulty methods
of preparation, may also be a determining factor on a border-line diet.

The diets which produce and cure pellagra have been examined by Wilson and their B.P.V.
determined. These values have been put together in a table, and sum­marise his
work upon the subject.

 

Pellagrous
Diets.

 

 

 

Available Protein.

B. P. V.

Animal Protein.

Calories.

Armenian    Refugee    Camp,

grams.

grams.

grams.

daily.

Port Said, May 1916

5i-5

23-0

4'°

2160

Goldberger's   Rankin   Farm

 

 

 

 

Experimental Diet .

35-o

i4-6

0-4

2836

Italian peasant, light labour

6o-i

3°*4

8-o

2020

Turkish   prisoners   of  
war,

 

 

 

 

Egypt, 1918 : non-labour

6o-o

33-5

IO'O

2825

hard-labour

63-0

36-8

137

2903

Egyptian
convicts :

 

 

 

 

light labour

69-5

33-5

60

3062

hard labour

827

48-3

22-8

3195

Abassia
Asylum

78-0

46-4

22-0

2910

Egyptian native boy aged n

29-0

10-4

O

1667

Diets which Cured Pellagra.1

 

Armenian
refugees

83-0

59-i

39\5

3M3

Egyptian
convicts, resting   .

827

547

29-4

2871

Egyptian native boy, aged n,

 

 

 

 

not resting

43'5

24-9

I4'5

 

Non-Pellagrous Diets.

 

Japanese
prisoners, 1911

English sewing-girl Scottish convicts,
hard labour Better-class English diet

390

62-0

105-0

91-6

37

45 66 80

0

(99
per

cent,
rice)

21-5

54'6

45

2110

2563 37°9 2681

1
Very advanced cases not cured.



QUALITY OF PROTEIN AND PELLAGRA    
113

The modern work on the quality of
protein gives the explanation of the insufficiency of gelatin as a food,
discovered during the French Revolution, and suggests that pellagra may have
existed in English gaols earty in the nineteenth century among
prisoners on a bread-and-water diet.  
During the  French  Revolution*food was scarce and gelatin was
extracted from bones and made into soup for the use of the poor and for
hospitals.   The soup was made palatable
with salt, vegetables and some­times a little meat.    Increased 
mortality followed its use and a commission was appointed to discover
the reason.   Some members of the
commission tried the soup and found its continued use caused indigestion,
nausea, burning thirst and diarrhoea.   
It was concluded that the soup contained insufficient nutriment and was
detrimental to health.   The physiologist
Magendie was appointed to make further investigations.   He fed dogs with gelatin ; they ate it
greedily at first, but it caused profuse diarrhoea. Dogs kept together soon
left the gelatin untouched and ate each other; if kept separately they refused
the gelatin but drank water.   Variations
in the flavouring made no difference.  
One dog, kept on bread and gelatin for 63 days, had profuse diarrhoea
all the time, but was cured in four days by changing the diet to meat.   Magendie considered that the diarrhoea was
directly due to the gelatin and not from the want of some elementary principle
in the diet.   Budd (1842) disagreed with
Magendie's verdict and attributed the symptoms to something wanting in the
diet, for he had been greatly impressed by the fre­quency with which diarrhoea
followed upon a bread-and-water diet in our prisons, and he mentioned
especially the  experiences  at 
Millbank  Penitentiary.   There, 
in July 1822, the ration was changed and the animal part of the diet
reduced almost to nothing.   In the
autumn the prisoners visibly declined—" those at the mill could grind less
corn, those at the pump could raise less water." In  the following spring, in  addition to much scurvy, 48 prisoners came
into hospital with diarrhoea of a peculiar 1



114   VITAMINS AND THE CHOICE OF FOOD

kind,
impaired digestion, diminished strength, various nervous symptoms and mental
despondency (cf. early symptoms
'#of pellagra, p. 91). Between 800 and 900 patients «ere affected in this
way; those longest in prisf n gunered most, except the officers and
staff and those rmsofters who assisted in the kitchens, all these escaped tne
illness. This exemption of certain groups in the same surroundings, but
with better food, suggests that the disease was the result of a food deficiency
and not of a contagious nature.

From these and similar experiences it became common knowledge that animal
food-stuffs had some special value in nutrition, and that gelatin, although a
nitrogenous animal product, was not a substitute for meat.

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