Dietary Properties of Vegetables


McCollum, Simmonds and Pitz * sought to test
the validity of the "vitamine" hypothesis in its
relation to scurvy, by an indirect method. The next
logical step in the investigation of the possible num-
ber of dietary essentials of unknown chemical nature
which occur in the growth-promoting fats (fat-
soluble A), and in the preparations which are never
associated with fats (water-soluble B), seemed to be
to study the oat kernel. There seemed much reason
to believe that this seed would prove to be unique
among the ordinary seeds in its dietary properties.
Theobald Smith 2 had, in 1895, called attention to the
fact that a diet of oats would cause in guinea pigs
the development of a condition suggestive of scurvy.
In 1909 Hoist and his co-workers in Sweden 3 de-
scribed numerous experiments involving the produc-
tion and relief of experimental scurvy in the guinea
pig. Hoist observed that when this animal is re-
stricted to a diet of oats it rarely fails to develop
scurvy within a few weeks. The disease which is so
produced is strikingly suggestive of scurvy in man.
There is pronounced swelling of the knee and elbow
joints, with rupture of the capillaries at these sites,


and there is also a spongy and hemorrhagic condition
of the gums.

Hoist stated that the disease was due to a deficiency
of the oat kernel in an antiscorbutic substance, which
is relatively unstable when manipulated in the lab-
oratory. Milk was stated to be efficient for the cure
of the disease induced by an oat diet, provided it was
raw or had not been heated to very high tempera-
tures. Milk which had been heated to 90° C. for
ten minutes was said to be still effective, but boiled
milk failed to induce a cure. Raw cabbage was
stated to be highly efficient as a remedy against
the disease in the guinea pig, whereas cooked or
dried cabbage had lost most of its antiscorbutic

In view of these observations, it seemed that, if
it were true that scurvy is as Funk and Hoist be-
lieved, a disease resulting from "vitamine" defi-
ciency, the oat kernel should prove to be a natural
food-stuff which lacked the antiscorbutic " vitamine''
but contained the anti-beri-bei i, and perhaps, also,
the anti-pellagra and other ' ' vitamines. ' ' McCollum,
Simmonds and Pitz 1 submitted the oat kernel to the
systematic procedure of the biological method of
analysis, feeding it as the sole source of nutriment,
and also with single and multiple additions of purified
food substances, employing the rat as the experi-
mental animal. This showed that the oat kernel
(rolled oats) can be supplemented by the addition of
a salt mixture of appropriate composition, a growth-


promoting fat, and the purified protein gelatin, so as
to induce growth at the maximum rate in young rats
from weaning time to the full adult size, and sup-
ported the production of a few young. When any
one of these additions is omitted, the animals fail to

The oat kernel, therefore, contains all the dietary
essentials in the water-soluble group (provided there
is more than one such substance). Like wheat it
lacks a sufficient amount of the fat-soluble A to
support normal nutrition. It was impossible to
harmonize the results described by Hoist in the
production of experimental scurvy in the guinea pig
with those of McCollum, Simmonds and Pitz, in
which the rat served as the experimental animal,
without making assumptions which would greatly
complicate the whole subject of nutrition investiga-
tions. There were serious discrepancies in the ex-
perimental data from different sources. Hoist's
studies pointed to the existence in the normal diet
of a substance or substances of unknown character,
which were easily destroyed by heat or by dessica-
tion, and which act as protective agents against
scurvy in the guinea pig, and appeared to demon-
strate that the supposed antiscorbutic substance or
substances were absent from the oat kernel. The
studies with the rat demonstrated beyond con-
troversy, that at least for the rat, the oat kernel is
deficient as a food only as respects the factors, in-
organic salts, fat-soluble A, and in a lesser degree in


the quality of its protein. When these factors are
corrected, the oat kernel becomes a complete food
for this species.

Scurvy has been produced experimentally by
faulty diet in the guinea pig, and is not known to
occur in any species other than man and the guinea
pig. If the explanation of Hoist and of Funk is cor-
rect that scurvy is the result of the lack of a specific
substance in the diet, it becomes necessary to make
the further assumption that man and the guinea pig
require this substance, since both suffer from the
disease, whereas other species, as the rat, do not re-
quire this complex as a dietary component. The
only alternative is to conclude that scurvy is in
realty not a " deficiency" disease in the sense in
which Funk and Hoist employed the term. That
there is actually no such unstable " antiscorbutic
substance' ' or " antiscorbutic vitamine" as postu-
lated by Hoist and Funk, has been demonstrated by
the studies of McCollum and Pitz. 4 The proof of
this is given in Chapter V. In the same chapter will
be discussed the other so-called "vitamine" deficiency
diseases, pellagra and rickets, and the character of
the diets which play a part in their etiology. The
data available supports the view that among the list
of so-called " deficiency " diseases, beri-beri, scurvy,
pellagra and rickets, only the first is due to the lack
of a specific protective substance, Funk's "vitamine,"
or water-soluble B in the diet. The others are at
least in some degree the result of faulty diets, but not


in the sense in which Funk and Hoist employed the
term " deficiency/ ' McCollum and Simmonds have
pointed out, however, that in the pathological con-
dition of the eyes, known as xerophthalmia, of dietary
origin mentioned above, we have a second deficiency
disease, analogous to beri-beri. 5 All the facts at
present available point, therefore, to the belief that
what McCollum and his co-workers term water-
soluble B, is in reality but a single physiologically
indispensable substance. 6 There is no evidence in
support of the view that the term fat-soluble A need
be considered as applying to more than a single
chemical substance. Xeropthalmia of dietary origin
will be described later (Chapter V).

Similarity of the Seeds from the Dietary Standpoint.
— By the application of the biological method
of analysis of a food-stuff to each of the more im-
portant seeds employed in the nutrition of man and
animals, the fact was brought to light that they all
resemble each other very closely in their dietary
properties. The list of seeds examined included, —
wheat, 7 corn, 8 rice, 17 rolled oats, rye, 9 barley, 9 kaffir
corn, 9 millet seed, 10 flaxseed, 10 pea 10 and both the
navy 11 and the soy bean. 9 These all contain proteins
which are of distinctly lower biological value for
growth than are the proteins of milk ; they all are too
poor in the same three inorganic elements, calcium,
sodium and chlorine. All are, with the exception of
millet seed, below the optimum in their content of
the dietary factor, fat-soluble A. These three diet-


aiy factors must be improved before any one of these
seeds becomes complete from the dietary stand-
point. The seeds are, therefore, to be classed to-
gether as regards their food values.

Since the seeds have the same faults from the diet-
ary standpoint, it is to be expected that when fed in
mixtures they should not supplement each other ex-
cept as regards the protein moiety. It would hardly
be expected that the proteins of two or more kinds
of seeds should be deficient in the same amino-acids,
and in the same degree, and feeding trials have shown
that mixtures of seeds furnish better protein values
for growth than do the single seeds when fed alone,
properly supplemented with respect to all other
factors. From the similarity of the inorganic con-
tent of all seeds, and their low content of the fat-
soluble A, it should be necessary to supplement any
mixture of seeds with respect to both these factors
before good nutrition can be secured. Experimental
trial shows this to be the case. It is not, therefore,
possible to secure appreciable growth in young animals
fed exclusively upon seed products as the sole source of

Casual observation teaches us that such animals
as the ox, horse, sheep and goat can grow and live
for years in a vigorous condition on diets derived
entirely from vegetable sources. After having un-
successfully attempted numerous times to induce
growth in animals fed strictly upon seed mixtures,
the thought naturally arose that there must be some


special properties in the leaves of the plant which
cause them to make good the dietary deficiencies of
the seeds. A careful inquiry in every possible direc-
tion failed to discover any animal which in its natu-
ral state limits its diet strictly to seeds. Birds all
appear to vary their diet of seeds with insects and
worms, and most birds eat to some extent of fruits
and certain tender leaves. All birds probably eat a
considerable amount of mineral substance in the
form of particles which they deliberately swallow,
and they secure in their natural state more or less of
all of the essential mineral elements in the drinking
water which has permeated the ground. These sup-
plemental sources of certain food substances, which
one is at first inclined to overlook, or if considered,
to regard as of an accessory nature, and therefore,
if " accessory," dispensable, are in reality of such
importance, that it is not too much to say that the
preservation of the species might turn upon the
opportunity or lack of opportunity to secure these

Among the omnivora, the author has been unable
to discover any species which subsists entirely upon
seeds. The hog is a typical omniverous feeder, but
it is well known to animal husbandrymen that there
are but two successful methods of pork production,
one of which is to feed growing pigs on grain while
they have access to a good pasture; the other is to
feed them milk, skim milk, or butter-milk, along
with a grain mixture. Ignorance of this fact has re-





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suited in enormous economic loss to farmers who
have attempted to keep growing pigs in a dry lot
and feed them cereal grains and by-products derived
from these, as the sole source of nutriment. Little
growth can be secured under these circumstances,
and the reason becomes clear from what has been
said above concerning the nature of the dietary
deficiencies of the seeds and the similarity of the
seeds from the dietary standpoint.*

It was a great surprise to McCollum, Simmonds
and Pitz 12 to find that appropriate mixtures of leaf
and seed make fairly satisfactory food mixtures for
the support of growth, whereas, as has been stated,
they were unable to secure any appreciable growth
in animals fed exclusively on seeds and seed products,
the drinking water supplied being distilled and there-
fore salt free. The first leaf which was studied was
that of the alfalfa plant, for the reason that the
ground, immature alfalfa plant is extensively ma]>
keted as a supplementary feed for pigs, and through
the courtesy of the Peters Milling Company of
Omaha, Nebraska a product " alfalfa flour' 9 was
made available in a convenient form. This consists

* It is not to be understood from this that it is intended to imply
that no increase in body weight can be secured in hogs when they are
confined strictly to grain mixtures. They may indeed become very
fat, and therefore apparently grow for a time on such foods as corn
alone. Even under farm conditions, where they are able to secure
a supplementary mineral supply through the water they drink and
through the consumption of soil with the grain, there is little growth
in the sense that the muscle and organ tissues increase in volume.

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of the dry, immature leaf of the plant ground to a
very fine powder of a bright green color.

A series of diets consisting of seed, 60 per cent,
and of alfalfa leaf flour, 40 per cent, were first
fed to growing rats. The seeds employed, included
wheat, corn, rolled oat, rye, millet seed, kaffir corn,
pea and bean. The degree of success in inducing
growth with most of these simple mixtures of one
seed with the alfalfa leaf is much greater than can ever
be secured with even such complex mixtures of seeds
as corn, wheat, oat, hemp seed and millet seed in
equal proportions. The latter mixture can support
a fair amount of growth when its inorganic defi-
ciencies are made good, but without mineral addi-
tions almost no growth can be secured. Chart 6
shows typical growth curves which give an accurate
idea of the relative values for growth of several
combinations of the alfalfa leaf with seeds. Among
the seeds with which studies have been made, the
oat is best supplemented by the alfalfa leaf. A
simple mixture of rolled oats, 60 per cent, and alfalfa
leaf, 40 per cent, induces nearly normal growth to
the adult size in the rat and induces a fair ampunt
of reproduction and rearing of young. However,
the animals fall considerably below the maximum
performance in both these respects.

An examination of other leaves of plants showed
that the latter can in a general way be classed to-
gether as food-stuffs of similar character, since they
resemble each other more or less closely, just as the

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seeds all resemble each other in their dietary prop-
erties. The leaf proves to be a very different thing
from the seed from the dietary standpoint. The dry
leaf usually contains from three to five times as
much total ash constituents as does the seed, and
is always especially rich in just those elements in
which the seed is poorest, viz., calcium, sodium and
chlorine. It follows, therefore, that the leaf supple-
ments the inorganic deficiencies of the seed. The
leaf, in most cases, contains much more of the dietary-
essential, fat-soluble A, than is found in any seed,
so that combinations of leaf and seed prove more
satisfactory for the nutrition of an animal than do
mixtures of seeds alone. The leaf contains protein
and amino-acids which result from digestion of pro-
teins as does the seed. The amount varies from 8
per cent of protein (nitrogen X 6.25) in such fleshy
leaves as the cabbage, after drying, to more than
15 per cent in the dry alfalfa or clover leaf. The
seeds vary in their content of protein from about 10
to 25 per cent. The leaf proteins appear, from
the data available, to supplement and enhance in
some degree the value of the seed proteins with which
they are combined. The leaf supplements, therefore,
all the nutritive deficiencies of the seed, but not
necessarily in a highly satisfactory manner.

It is interesting to reflect upon the reasons why
the leaf of the plant should show such decided dif-
ferences in its nutritive properties as contrasted
with the seed. A consideration of the difference in


function of the two gives the clue to the cause. The
seed consists of a germ, which forms in most cases
but a very small part of the entire seed, together
with a relatively large endosperm. The germ con-
sists of living cells, which respire and are capable of
multiplication (germination) when the conditions
are favorable. In the wheat kernel the germ con-
stitutes about 5 per cent of the entire seed. The
endosperm, on the other hand, consists largely of
reserve food materials such as protein, starch,
sugars, fats and mineral salts. It is not living matter,
and contains few cellular elements. The endosperm
is, therefore, in most respects comparable to a mix-
ture of purified food-stuffs. There is, as experiments
have abundantly demonstrated, relatively little of
the dietary factor, water-soluble B, in the endosperm,
and relatively much in the germ or embryo. The
same is true for the second unidentified dietary
factor fat-soluble A. This is practically absent from
the endosperm, but is fairly abundant in the germ.
Since the latter represents so small a portion of the
entire seed, the seed itself is too poor in this sub-
stance, in nearly all cases, to supply the needs of a
growing animal.

The leaf of the plant, on the other hand, is very
rich in cells, and in most cases contains but little re-
serve food material. It is the laboratory of the plant.
Chlorophyll, its green pigment, enables it to make
use of the energy of the sunlight, and from the
carbonic acid gas which it absorbs from the air,

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together with water and mineral salts, which it
absorbs from the soil through its roots, it builds
up proteins, starch, sugars and fats, which are used
for the growth of new plant tissue, or for storage in
the seed, tuber or other storage organs. The sur-
faces of the leaf are a mosaic of living cells. They
contain all the chemical complexes which are nec-
essary for the nutrition of the animal cells, and are
qualitatively complete foods.

The quality of the leaf from the dietary standpoint
may vary to a considerable extent. Some leaves are
thin cellular structures, which dry easily in the sun
when separated from the plant. In others, as the
cabbage, the leaf is in some degree modified as a
storage organ, and contains a considerable amount
of sugars. The cabbage leaf likewise contains more
than the ordinary amount of cellulose, which is its
skeletal tissue. Its dietary properties are modified
by these peculiarities in that the cellular elements
are diluted by the more inert tissues and reserve
food substances in the leaf. The freer a leaf is from
the function of a storage tissue, the more intensified
will be its leaf properties as a food. The fleshy leaves
tend to have in some degree the dietary properties
of the seed, and stand intermediate between the
leaves, which are thin, and dry easily, and the seed
in this respect.

The Tubers. — After the seeds, the tubers of cer-
tain plants constitute one of the most important
classes of energy-yielding foods. The potato and


sweet potato are by far the most important rep-
resentatives of this group in Europe and the Ameiv
icas, but several other kinds of tubers are widely
used as human food in the Orient. An examination
of the potato has been recently made, which reveals
the special dietary properties of this tuber to be just
what we should expect from its function as a storage
organ for reserve food in the plant. The functions
of the potato are twofold, viz., to reproduce the
plant in the Mowing generation, and to furnish
a food supply for the young potato plantlet while
it is developing root and leaf systems which make
it independent of the food stored in the old tuber.
The "eyes" of the potato represent groups of cells
which are analogous to the germ of the seed. These
are the points at which the potato sprouts when the
conditions are appropriate. There is underneath
the skin of the potato a layer of cells which are alive
and respiring during the life of the tuber, but the
interior of the potato consists almost entirely of
water, starch, protein, and to some extent of mineral
salts. The cellular structures in the interior are
gorged with starch, etc., and this portion is therefore
analogous in its dietary properties with the endo-
sperm of the seed. Both are comparable to a mixture
of purified protein, carbohydrate, and salts, which,
as we have previously seen, is not capable of support-
ing life. This portion, like the portion of the rice
kernel, which remains after polishing, is almost
lacking in both the chemically unidentified dietary


essentials, fat-soluble A and water-soluble B, and
accordingly cannot support life even though it may
have an appropriate chemical composition as shown
by analysis. The potato is to be classed with the
seeds in its dietary properties, because it consists
largely of reserve food materials and relatively little
of cellular elements. The results available indicate
that if the potato is steamed and the thin paperlike
skin removed without the loss of the cellular layer
which lies just underneath, it will contain relatively
f more of the fat-soluble A, a lack of which leads to
the development of the peculiar eye conditions pre-
viously described, than do the cereal grains. Al-
though it has not been subjected to experimental
test, it would seem that a potato which is pared in
the ordinary way and the paring discarded, is
changed in its dietary properties in much the same
way as is the rice kernel during the polishing process.
In the latter, the germ and the bran layer are both
rubbed off, leaving the endosperm without the small
quota of cellular elements which it possessed in its
natural state, and is correspondingly changed in its
food value (see legend to Chart 3). The protein of
the potato is not quite so valuable for growth as that
of the cereal grains when fed as the sole source of
this dietary factor. 9

There have been a number of experiments of short
duration which gave results which indicate that in
the human subject the nitrogen of the potato is of
extraordinary value for replacing that lost through


daily metabolism in the adult. McCollum, Sim-
monds and Parsons, have tested this question by
comparing with the protein of the cereal grains the
value of the nitrogen of the potato when this tuber
was supplemented in such a manner as to make
good all of its deficiencies except protein. The
experiments involved growth tests in the young rat.
The results show conclusively that potato nitrogen
falls considerably below the value for growth pos-
sessed by the individual cereal grains, when each of
these serves as the sole supply of the digestion prod-
ucts of protein.

The Roots Employed as Food. — The same rea-
soning applies to the root crops as to the potato,
with respect to the relation between dietary prop-
erties and biological function. The roots which we
employ as food are those which are highly modified
as storage organs, and resemble the potato in con-
taining a very high water and starch content, and
but very little protein. Like the potato, there is a cel-
lular layer at the periphery, and the interior is loaded
with reserve food-stuffs. Appropriate feeding tests
have shown that the properties of the beet resemble
those of the seed and the tuber, rather than those of
the leaf. 9 The fleshy roots and the potato and the
sweet potato have an inorganic content which re-
sembles that of the seed in a general way, so that an
inspection of the analytical data relating to the
composition of the ash of the seeds, tubers and roots,
gave no promise that the combination in diets of


seeds with either of the latter classes of food-stuffs
would correct the inorganic deficiencies of the former.
Feeding experiments in which a seed and a tuber
were combined, and so supplemented with purified
protein, and fat-soluble A (in butter-fat), that all
the deficiencies of the mixture, except the inorganic,
were made good, have shown that in the combinations
of each of the more important seeds with the potato,
the resulting mineral supply, which is derived solely
from the natural foods themselves, is not of a char-
acter suitable for the support of growth. 9 The con-
tent of the elements, calcium, sodium and chlorine
must be augumented by greater amounts before such
food mixtures are complete with respect to their
mineral content. No studies have as yet been made
to determine the biological value of the nitrogen of
the tubers other than the potato, and none at all of
the edible roots.

From the results of systematic feeding trials with
mixtures of seeds alone and the same with single and
multiple purified food additions, and the same type
of experiment using certain of the tubers and root
foods in place of the seeds, it is shown that all these
classes of foodstuffs resemble one another in all re-
spects except in the high content of water in the
tubers and roots. In the dry state they are all much
like the seeds, but there is one minor difference which
should be mentioned. The most important difference
lies in the character of the nitrogenous compounds.
In the seeds the nitrogen is almost all contained in

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the form of true protein. In the tubers and edible
roots most of it is in the form of much simpler com-
pounds, a part being the same amino-acids which are
derived from proteins on digestion.

It is possible to prepare diets derived solely from
vegetable products which will nourish an animal
during growth and throughout life in a very satis-
factory manner, but it is a surprisingly difficult task
to prepare for the omnivera, an adequate diet com-
posed entirely of food-stuffs of plant origin. While
many of the seeds contain nothing of a detrimental
character, many of the leaves, when eaten, undoubt-
edly do introduce into the body substances which
have more or less injurious effects. The nature of
these cannot be stated at the present time, but the
possibility that there may be an injurious effect
brought about by prolonged administration of such
bodies as the tannins, the glucosides and oxalic acid,
certain organic bases which in some cases resemble
certain of the alkaloids, and in some leaves the pres-
ence of alkaloids which are highly active pharmaco-
logically, can easily account for the fact that with
all rations of strictly vegetable origin one would
not have optimum nutrition. McCollum and Sim-
mon ds have in a long list of trials with mixtures of
leaves and seeds been unable to secure the opti-
mum of well-being in omnivorous animals. It is
worthy of the greatest emphasis that in our hundreds of
trials with diets derived entirely from vegetable sources,
we have not succeeded in producing optimum results in


the nutrition of an omnivorous animal the rat. Certain
of the animals which we have restricted to foods of
plant origin, have done so well that we should in the
absence of much experience with diets of excellent
quality, have considered them to be normal in every
respect. It should be emphasized that the average
performance of a group of people or animals living
upon a varied diet cannot safely be assumed to repre-
sent the best of which they are capable. In the
study of diets the author and his colleagues have
kept constantly in mind the best results we have ever
seen in the nutrition of animals, as exemplified in
rapidity of growth, ultimate size attained, number of
young produced, and the success with which these
were reared, and have attempted to assign to every
experimental group its legitimate place on a scale of
performance, which has complete failure to either
grow or long remain alive as the one extreme, and
the optimum of which the animal is capable as the

In connection with the statement which has just
been made regarding the strict vegetarian diet, that
it does not, so far as has been observed, induce the
best results in the nutrition of the omnivora, it should
be added that in human dietary practice what is
generally designated as vegetarianism is in reality
something very different. Many people bold that
they are adhering to vegetarian dietary habits, who
in reality, take in addition to foods of plant origin,
milk or eggs or both. This type of diet will give very


much better results than can be secured from the
use of vegetable foods alone. Lacto-vegetarianism
should not be confuesd with strict vegetarianism.
The former is, when the diet is properly planned,
the most highly satisfactory plan which can be
adopted in the nutrition of man. The latter, if
strictly adhered to, is fraught with grave danger
unless the diet is planned by one who has extensive
and exact knowledge of the special properties of the
various food-stuffs employed.

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